rightscale.sever_array.Execute actor integration tests.
Properly handle missing RightScale Script response (None).
Handle two additional rightscale.server_array.Execute failure modes better.

1. If the RightScript doesn't exist, throw a reasonable exception.
2. If the Inputs are incorrectly formatted, throw a reasonable
exception.

For both cases, implement integration and unit tests.
Merge branch 'master' of github.com:Nextdoor/kingpin into execute_integration_tests
Typo fix
Merge pull request #19 from Nextdoor/execute_integration_tests

rightscale.sever_array.Execute actor integration tests.