Reorganize tests/cmd

This commit reorganizes the 'cmd' tests by subcommand.

Previously the multipath test was using an actual fixture directory
which actually made the fixtures directory somewhat unusable by other
tests since with an upcoming change (get_plugins_version) fixtures
directories may also contain YAML that doesn't contain JJB data.

Change-Id: I4c3866e1e0769512b40e1790e40affedb13953a2
Merge "Reorganize tests/cmd"