Upgrade terraform to 0.13.7

[stoyanr]

How to categorize this PR?

/area control-plane
/kind enhancement

What this PR does / why we need it:
Upgrades terraform to 0.13.7. This is the first step of upgrading to 0.15 in order to fix gardener/gardener/issues/4838.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

• I ran successfully make test-e2e and make docker-images locally.
• I also ran successfully make start and make start COMMAND=destroy with a valid AWS configuration for one of my test shoots.
• For the provider validation status, see the comment below.

Release note:

terraform has been upgraded to 0.13.7

[stoyanr]

/invite @ialidzhikov

[stoyanr]

Provider validation status:

AWS (see gardener/gardener-extension-provider-aws/pull/439):

• reconciliation and deletion of existing Infrastructure
• creation and deletion of new Infrastructure (single zone, new vpc)
• creation and deletion of new Infrastructure (single zone, existing vpc)
• creation and deletion of new Infrastructure (multiple zones, new vpc)
• creation and deletion of new Infrastructure (multiple zone, existing vpc)
• gardener-extension-provider-aws Infrastructure integration test

GCP (see gardener/gardener-extension-provider-gcp/pull/345):

• reconciliation and deletion of existing Infrastructure
• creation and deletion of new Infrastructure (single zone, new vpc)
• creation and deletion of new Infrastructure (single zone, existing vpc)
• gardener-extension-provider-gcp Infrastructure integration test

Azure (see gardener/gardener-extension-provider-azure/pull/391):

• reconciliation and deletion of existing Infrastructure
• creation and deletion of new Infrastructure

Alicloud (see gardener/gardener-extension-provider-alicloud/pull/379):

• reconciliation and deletion of existing Infrastructure
• creation and deletion of new Infrastructure

Openstack (see gardener/gardener-extension-provider-openstack/pull/350):

• reconciliation and deletion of existing Infrastructure
• creation and deletion of new Infrastructure

[ialidzhikov]

We had a sync with @stoyanr on how to proceed with the terraform version updates. We agreed to proceed first with the 0.13.7 update and to have a new terraformer minor release with it (terraformer@v2.13.0). When provider extensions successfully adopt terraformer@v2.13.0, we plan to proceed with the 0.14.11 and 0.15.5 updates in new minor releases - 0.14.11 update in terraformer@v2.14.0 and 0.15.5 update terraformer@2.15.0. Meanwhile, if we need to do critical corrections, we will do it with patch releases of the corresponding terraformer minor release (for example provider-aws wants to update its terraformer-provider-aws - this can be performed with v2.13.1, v2.14.1 or v2.15.1 depending on which version of the terraformer is used currently by the provider-aws extesion).
We also agreed that gardener/gardener#4978 is important for debugging and investigation purposes and it will be good if release of provider extension adopts terraform version bump together with a fix for gardener/gardener#4978.

Last but not least, many thanks to @stoyanr for his work on this topic.
I will need some time to get familiar with the details and to run some basic tests also on my side.

/cc @rfranzke @dkistner @kon-angelo

[ialidzhikov]

Looks good to me in general. I managed to test the following scenarios with gardener-extension-provider-aws and they worked well:

• reconciliation of existing Infrastructure
• deletion of existing Infrastructure
• creation and deletion of new Infrastructure (single zone, new vpc)
• creation and deletion of new Infrastructure (multiple zones, new vpc)
• creation and deletion of new Infrastructure (single zone, existing vpc)
• creation and deletion of new Infrastructure (multiple zone, existing vpc)

[stoyanr]

@ialidzhikov I added the tests as requested and replied to your other comments, PTAL.

[ialidzhikov]

/lgtm