🐛 Don't require cinder when not using volumes

[mdbooth]

What this PR does / why we need it:

The addition of multi-AZ volume support inadvertently added a hard requirement for Cinder. This change removes that requirement by:

• Splitting ComputeClient into separate Compute, Image, and Volume clients
• Making initialisation of each client lazy on first use

If a machine definition does not use volumes the VolumeClient will not be initialised, meaning Cinder is no longer a requirement.

Which issue(s) this PR fixes:
Fixes #1345

Special notes for your reviewer:

It might be simpler to review these 2 commits separately. I pulled the first one out of one of my other outstanding PRs #1236. The separation of clients which I did in that PR for other reasons works very nicely for this, too.

The first commit is mostly code motion. The second commit implements the change.

/hold

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mdbooth

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• OWNERS [mdbooth]

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[jichenjc]

I like the idea , create such error client should help abstract the error case

[mdbooth]

I wanted to create a proper monad, but that's not ergonomic in Go. This seemed like a fairly neat alternative.

[jichenjc]

/lgtm

[mdbooth]

/hold cancel

[mdbooth]

@jichenjc Had to fix a couple of merge conflicts, but nothing consequential. Appreciate it if you could have a look and restore your lgtm.

[jichenjc]

/lgtm
/hold

lgtm, hold this wait for CI and please unhold when you think it's ok after CI pass @mdbooth

[mdbooth]

/hold cancel

[tobiasgiese]

lgtm, hold this wait for CI and please unhold when you think it's ok after CI pass @mdbooth

@jichenjc Prow will not merge until the required tests are green 🙂 thus, there is no need to add the hold to wait for CI to pass. Just FYI

[jichenjc]

@tobiasgiese thanks :)

[jichenjc]

/cherry-pick release-0.6

[k8s-infra-cherrypick-robot]

@jichenjc: #1353 failed to apply on top of branch "release-0.6":

Applying: Move clients into a separate package
Using index info to reconstruct a base tree...
M	pkg/cloud/services/compute/client.go
M	pkg/cloud/services/compute/client_mock.go
M	pkg/cloud/services/compute/instance.go
M	pkg/cloud/services/compute/instance_test.go
M	pkg/cloud/services/compute/instance_types.go
M	pkg/cloud/services/compute/instance_types_test.go
M	pkg/cloud/services/compute/service.go
M	pkg/cloud/services/loadbalancer/client.go
M	pkg/cloud/services/loadbalancer/loadbalancer_test.go
A	pkg/cloud/services/loadbalancer/mock_loadbalancer/doc.go
M	pkg/cloud/services/loadbalancer/mock_loadbalancer/loadbalancer_service_mock.go
M	pkg/cloud/services/loadbalancer/service.go
M	pkg/cloud/services/networking/client.go
M	pkg/cloud/services/networking/floatingip_test.go
M	pkg/cloud/services/networking/mock_networking/client_mock.go
M	pkg/cloud/services/networking/mock_networking/doc.go
M	pkg/cloud/services/networking/port_test.go
M	pkg/cloud/services/networking/service.go
M	pkg/cloud/services/networking/trunk_test.go
M	test/e2e/shared/openstack.go
Falling back to patching base and 3-way merge...
Auto-merging test/e2e/shared/openstack.go
CONFLICT (content): Merge conflict in test/e2e/shared/openstack.go
Auto-merging pkg/cloud/services/networking/trunk_test.go
CONFLICT (content): Merge conflict in pkg/cloud/services/networking/trunk_test.go
Auto-merging pkg/cloud/services/networking/service.go
Auto-merging pkg/cloud/services/networking/port_test.go
CONFLICT (content): Merge conflict in pkg/cloud/services/networking/port_test.go
CONFLICT (modify/delete): pkg/cloud/services/networking/mock_networking/doc.go deleted in Move clients into a separate package and modified in HEAD. Version HEAD of pkg/cloud/services/networking/mock_networking/doc.go left in tree.
Auto-merging pkg/cloud/services/networking/floatingip_test.go
CONFLICT (content): Merge conflict in pkg/cloud/services/networking/floatingip_test.go
Auto-merging pkg/cloud/services/loadbalancer/service.go
Auto-merging pkg/cloud/services/loadbalancer/loadbalancer_test.go
CONFLICT (content): Merge conflict in pkg/cloud/services/loadbalancer/loadbalancer_test.go
Auto-merging pkg/cloud/services/compute/service.go
Auto-merging pkg/cloud/services/compute/instance_types_test.go
Auto-merging pkg/cloud/services/compute/instance_types.go
CONFLICT (content): Merge conflict in pkg/cloud/services/compute/instance_types.go
Auto-merging pkg/cloud/services/compute/instance_test.go
CONFLICT (content): Merge conflict in pkg/cloud/services/compute/instance_test.go
Auto-merging pkg/cloud/services/compute/instance.go
CONFLICT (content): Merge conflict in pkg/cloud/services/compute/instance.go
Auto-merging pkg/clients/networking.go
Auto-merging pkg/clients/mock/network.go
Auto-merging pkg/clients/mock/loadbalancer.go
Auto-merging pkg/clients/mock/compute.go
Auto-merging pkg/clients/loadbalancer.go
CONFLICT (content): Merge conflict in pkg/clients/loadbalancer.go
Auto-merging pkg/clients/compute.go
CONFLICT (rename/delete): pkg/cloud/services/loadbalancer/mock_loadbalancer/doc.go deleted in Move clients into a separate package and renamed to hack/boilerplate/boilerplate.generatego.txt in HEAD. Version HEAD of hack/boilerplate/boilerplate.generatego.txt left in tree.
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 Move clients into a separate package
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

In response to this:

/cherry-pick release-0.6

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[jichenjc]

plan to cherry pick this for 0.6 but encounter many conflict ...