classify tests and extend coverage

[clux]

This pr clarifies the distinction between our different types of tests and writes a policy on when to write a test for what. The key change for that is in the new CONTRIBUTING.md.

Classification: integration reclassified as e2e. New integration is cargo test --ignored (using a live Client)

New tests

Some tests imported and re-purposed from examples with new invariants:

• integration tests use disjoint set of objects
• integration tests now can run in parallel

This lets us improve the coverage without having to build the very expensive example setup with tarpaulin (and also lets us potentially run this class of tests more easily across clusters).

Coverage Improvements

Almost a 10% bump locally. After merge: (NB: it doesn't count derive very well, so it's still misleading).

• kube-client/src/lib.rs -> integration tests that need client and core (web sockets, pod creation, api usage, discovery)
• kube/src/lib.rs -> integration tests that need a combination of runtime, derive, and client (crd usage, crd discovery)

Also some more sporadic integration tests in runtime's eventrecorder.

Test Policy

We need a test policy and proof that we uphold a test policy in general for #737 and this should be sufficient for the policy, and pointing at a constant line/upward trend on coverage should be enough to prove it is upheld.

[codecov-commenter]

Codecov Report

Merging #745 (d6ed190) into master (3e92a67) will increase coverage by 9.85%.
The diff coverage is 94.51%.

❗ Current head d6ed190 differs from pull request most recent head e2c6201. Consider uploading reports for the commit e2c6201 to get more accurate results

@@            Coverage Diff             @@
##           master     #745      +/-   ##
==========================================
+ Coverage   60.34%   70.19%   +9.85%     
==========================================
  Files          52       53       +1     
  Lines        3051     3352     +301     
==========================================
+ Hits         1841     2353     +512     
+ Misses       1210      999     -211     

Impacted Files	Coverage Δ
kube-runtime/src/wait.rs	35.71% <0.00%> (+1.56%)	⬆️
kube-client/src/lib.rs	92.74% <92.74%> (ø)
kube-runtime/src/events.rs	92.45% <94.73%> (+92.45%)	⬆️
kube/src/lib.rs	97.72% <96.82%> (-2.28%)	⬇️
kube-core/src/object.rs	76.66% <100.00%> (+43.33%)	⬆️
kube-core/src/subresource.rs	75.72% <100.00%> (+16.78%)	⬆️
kube-core/src/util.rs	100.00% <100.00%> (+100.00%)	⬆️
kube-core/src/dynamic.rs	66.66% <0.00%> (-4.77%)	⬇️
kube-core/src/request.rs	95.00% <0.00%> (+0.38%)	⬆️
... and 17 more

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[kazk]

I'll remove the requirement for integration check, and add e2e.

EDIT: Done

[clux]

Ok, perfect. I am ready to merge this if you are happy with it.