Bug 1013321 - Handle implicit arguments more accurately

When both arguments to a command are optional (rhc ssh <app> <command...>), if the user wants to use the default app - the current Git directory, for instance - then they must specify '--' in order to guarantee that <command> isn't confused for <app>.  This commit changes that parsing behavior and cleans up the tests to ensure we are covering that case.
domain.feature fails because rhc domain changes

Also allow RHC_DEBUG=<path> to log output during execution
Review comments, add more tests and fix a few edge cases
Merge pull request #471 from smarterclayton/bug_1013321_handle_implicit_arguments_correctly

Merged by openshift-bot