Add support for helm --force flag

[tjerkw]

We're using skaffold and helm to deploy. In our ci-cluster deploys sometimes fail,
but then skaffold cannot install it anymore if it finds a failed helm installation.
The --force flag solves this.

See the --force functionailtiy added in helm 2.5.0:
helm/helm#2280

Potential solution for #1328
Makes it more easy to use skaffold in a ci-pipeline. (deploy from a clean sheet)

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[tjerkw]

I signed it!

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CLAs look good, thanks!

[codecov-io]

Codecov Report

Merging #1499 into master will decrease coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1499      +/-   ##
==========================================
- Coverage   44.87%   44.85%   -0.02%     
==========================================
  Files         115      115              
  Lines        4771     4773       +2     
==========================================
  Hits         2141     2141              
- Misses       2409     2410       +1     
- Partials      221      222       +1

Impacted Files	Coverage Δ
pkg/skaffold/deploy/helm.go	64.09% <0%> (-0.59%)	⬇️

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[priyawadhwa]

Just one comment, but once that is addressed this should be ready!

[priyawadhwa]

So, unfortunately because of the way we have to release config changes, this change also needs to be made in integration/examples/annotated-skaffold.yaml. Would you mind adding it there as well? Thanks!

[tjerkw]

As agreed here, lets use the flag based approach:
#1506