Integration test command

[daddz]

I have put some more work into this as mentioned in #2561.

For demonstration purposes I created another repository that makes use of these changes over here: https://github.com/daddz/skaffold-integration

When running the integrationtest command it will try to find the first pod that matches the defined podSelector and then executes the specified testCommand via kubectl exec in that pod.

[codecov]

Codecov Report

Merging #2594 into master will decrease coverage by 0.15%.
The diff coverage is 45.61%.

Impacted Files	Coverage Δ
pkg/skaffold/schema/versions.go	74.35% <ø> (ø)	⬆️
pkg/skaffold/runner/runner.go	0% <ø> (ø)	⬆️
pkg/skaffold/schema/v1beta12/upgrade.go	100% <ø> (ø)	⬆️
pkg/skaffold/schema/latest/config.go	100% <ø> (ø)	⬆️
pkg/skaffold/runner/build_deploy.go	64.17% <0%> (-4.08%)	⬇️
pkg/skaffold/integrationtest/integrationtest.go	0% <0%> (ø)
pkg/skaffold/schema/v1beta13/config.go	100% <100%> (ø)
pkg/skaffold/schema/defaults/defaults.go	90.66% <100%> (+0.25%)	⬆️
cmd/skaffold/app/cmd/cmd.go	68.5% <100%> (+0.24%)	⬆️
pkg/skaffold/schema/v1beta13/upgrade.go	100% <100%> (ø)
... and 6 more

[tejal29]

@daddz Thank you for your contribution.
You are adding a new Command to skaffold and we now have a process to add new features.
Its is documented here https://github.com/GoogleContainerTools/skaffold/tree/master/docs/design_proposals

Can you please add a DD for this feature? Please feel free to add me as a Design Shepherd.

[daddz]

@tejal29 thanks for the feedback!
I addressed your comments and created a design proposal: #2671