replace log with glog for all tests

[jessiezcc]

Fixes #1066, #763

• replace log with glog for all tests
• update document with glog instructions

[google-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jessiezcc

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:

• test/OWNERS [jessiezcc]

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

[dprotaso]

I'd like to be consistent and use the same logger within the whole project/repo. Thus not use glog but zap

These PRs is where the work was done for the controllers:
#998
#978
#933
#888

thoughts?

[jessiezcc]

@dprotaso, we are leveraging glog VLog for verbose logs, and also get underlying k8s V logs for free, does zap have similar capability?
Also chatted with Mustafa (mdemirhan@), sounds like with zap, there is also extra work for log readability, and we still need glog to get k8s outputs, so I think glog alone should satisfy our test log need for now.

[jessiezcc]

Actually, I'm opening a separate issue to track further about how test log can leverage zap structured log for better failure troubleshooting. Mustafa listed a few goodness of structured log that's beneficial for test failure diagnose. Would like to get this one in first though.

[mattmoor]

Havent cracked the diff here, but generally I share @dprotaso's sentiment. We decided to go with zap, so let's go with zap.

[jessiezcc]

I've created #1117 to track using zap in test log. My plan is to get this one merged first. Also it will take more than a week for me to get zap change in as I will be away at summit for almost a week (coming week). Let me know if you have string objections on having this PR merged, @mattmoor @dprotaso .

[adrcunha]

/lgtm

[adrcunha]

/test pull-knative-serving-integration-tests