add kubectl checks to limits:set tests

[Cryptophobia]

From @bacongobbler on March 8, 2016 23:26

As per https://github.com/deis/workflow-e2e/blob/003e0e6b12398707174caad8cdb556e8227cce3f/tests/limits_test.go#L10, we need to add checks to kubernetes to validate that the correct limits have been applied to the deployed pods.

Copied from original issue: deis/workflow-e2e#92

[Cryptophobia]

From @mboersma on March 16, 2016 16:8

The tags_test.go now uses kubectl successfully--the only hitch was resetting $HOME to the original user so that the proper configuration is found. The kubectl code there provides an example that might be useful here.