(WIP) feature: Drain nodes prior to termination when using RollingUpgrade strategy

[eytan-avisror]

Adds to #197

This feature adds a capability to do draining in parallel via kubectl as a library (not shelling out), prior to termination of instances.

This makes the rollingUpgrade strategy much more usable.

Implementation adds a sync.Map of namespacedName : sync.WaitGroup at the controller level in order to keep track of draining nodes.

The drain is initiated and then the controller will re-queue until operation has completed or errors out.
Also refactored to move the rollingUpgrade logic from kubeprovider into the eks package.

TBD:

• Write unit tests
• Test edge cases (PDB, drain error, autoscaler, etc)

[codecov]

Codecov Report

Merging #259 (8b35ea4) into master (165095e) will increase coverage by 34.28%.
The diff coverage is 52.76%.

❗ Current head 8b35ea4 differs from pull request most recent head 7a3066f. Consider uploading reports for the commit 7a3066f to get more accurate results

@@             Coverage Diff             @@
##           master     #259       +/-   ##
===========================================
+ Coverage   51.08%   85.37%   +34.28%     
===========================================
  Files          33       18       -15     
  Lines        4504     2345     -2159     
===========================================
- Hits         2301     2002      -299     
+ Misses       2062      237     -1825     
+ Partials      141      106       -35     

Impacted Files	Coverage Δ
controllers/provisioners/eks/update.go	82.12% <ø> (+2.30%)	⬆️
controllers/provisioners/provisioners.go	100.00% <ø> (ø)
controllers/provisioners/eks/rollingupdate.go	52.20% <52.20%> (ø)
controllers/provisioners/eks/upgrade.go	91.11% <66.66%> (+6.14%)	⬆️
controllers/provisioners/eks/eks.go	84.61% <100.00%> (-2.62%)	⬇️
controllers/provisioners/config.go	70.90% <0.00%> (-6.20%)	⬇️
controllers/provisioners/eks/cloud.go	83.92% <0.00%> (-2.15%)	⬇️
...ntrollers/provisioners/eks/scaling/launchconfig.go	91.97% <0.00%> (-0.64%)	⬇️
... and 24 more

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