Merge global and context-specific array settings in Skaffold config

[corneliusweig]

See #2554 for details and discussion.

Depends on #2555

[nkubala]

@corneliusweig #2555 has been merged, can you rebase this one and then make it ready for review?

[corneliusweig]

@nkubala Rebase is done, now let's wait for the CI.

[codecov]

Codecov Report

Merging #2590 into master will increase coverage by 0.28%.
The diff coverage is 0%.

Impacted Files	Coverage Δ
pkg/skaffold/config/util.go	63.29% <0%> (ø)	⬆️
pkg/skaffold/kubernetes/client.go	40% <0%> (-18.83%)	⬇️
pkg/skaffold/test/test.go	94.28% <0%> (-5.72%)	⬇️
...g/skaffold/kubernetes/portforward/pod_forwarder.go	85.48% <0%> (-1.48%)	⬇️
pkg/skaffold/kubernetes/context/context.go	100% <0%> (ø)	⬆️
pkg/skaffold/test/structure/types.go	100% <0%> (ø)	⬆️
...ffold/kubernetes/portforward/port_forward_entry.go	100% <0%> (ø)	⬆️
cmd/skaffold/app/cmd/flags.go	100% <0%> (ø)	⬆️
...kubernetes/portforward/port_forward_integration.go	0% <0%> (ø)	⬆️
pkg/skaffold/config/options.go	100% <0%> (ø)	⬆️
... and 3 more

[nkubala]

@corneliusweig ignore the failing travis build, we switched to a different travis host while this PR was open so that one will always fail, this one is good to go!