feat(config.py): Add ability to setup default tags for applications

[rvadim]

We have big enough k8s cluster with many nodes, some parts of nodes very specific and also have specific labels (another version of docker, perf test nodes, etc). So in this situation all of our users need to set tag like "role=worker", it's not very good. And sometimes we detect applications w/o tags working on nodes where it should not.

docs: https://github.com/deis/workflow/pull/750

[deis-admin]

Thanks for the contribution! Please ensure your commits follow our style guide. This code will be tested once a Deis maintainer reviews it.

[codecov-io]

Codecov Report

Merging #1249 into master will increase coverage by 0.03%. The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master    #1249      +/-   ##
==========================================
+ Coverage   87.21%   87.25%   +0.03%     
==========================================
  Files          44       44              
  Lines        3873     3883      +10     
  Branches      673      674       +1     
==========================================
+ Hits         3378     3388      +10     
- Misses        326      327       +1     
+ Partials      169      168       -1

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[mboersma]

Jenkins, add to whitelist.

[vdice]

Also, rebase needed it appears.

[vdice]

Jenkins, test this please.

[vdice]

Apologies, @rvadim -- master branch in controller was broken for a short amount of time -- a quick rebase is needed (should be trivial) and then we can kick off CI again.

[rvadim]

Rebase done, thank you for review.