Fix labelling panic for prepackaged servers

[ukclivecox]

Fixes #1599

• Checks for nil pu.type in labels method
• Defaults prepackaged servers to MODEL type in defaulting
• Adds a test for checking prepackaged model servers are defaulted correctly

[ukclivecox]

/test integration

[seldondev]

Wed Mar 25 15:35:46 UTC 2020
The logs for [lint] [2] will show after the pipeline context has finished.
https://github.com/SeldonIO/seldon-core/blob/gh-pages/jenkins-x/logs/SeldonIO/seldon-core/PR-1600/2.log

impatient try
jx get build logs SeldonIO/seldon-core/PR-1600 --build=2

[seldondev]

Wed Mar 25 15:36:30 UTC 2020
The logs for [integration] [3] will show after the pipeline context has finished.
https://github.com/SeldonIO/seldon-core/blob/gh-pages/jenkins-x/logs/SeldonIO/seldon-core/PR-1600/3.log

impatient try
jx get build logs SeldonIO/seldon-core/PR-1600 --build=3

[seldondev]

Wed Mar 25 15:37:07 UTC 2020
The logs for [pr-build] [1] will show after the pipeline context has finished.
https://github.com/SeldonIO/seldon-core/blob/gh-pages/jenkins-x/logs/SeldonIO/seldon-core/PR-1600/1.log

impatient try
jx get build logs SeldonIO/seldon-core/PR-1600 --build=1

[adriangonz]

/approve

Looks good to me!

[seldondev]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: adriangonz

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [adriangonz]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[seldondev]

@cliveseldon: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
integration	62a758e	link	/test integration

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. I understand the commands that are listed here.

[adriangonz]

The failed test is one of the Ambassador rolling update tests. We could merge regardless of that one @cliveseldon?

[adriangonz]

It would be good to consider bumping up the flaky tests attempts though.