Add CLI tests for tag plugin

Fix https://trac.openmicroscopy.org.uk/ome/ticket/11466

This PR adds new integration tests for the recent tag CLI plugin added by @criswell (see #1389).
Additionally this PR adds some basic framework for adding new integration CLI tests by defining a `CLITest` class inherited from ITest.

To test this PR, check the new clitests are listed in the daily integration build test report, http://hudson.openmicroscopy.org.uk/job/OmeroPy-integration-develop/lastCompletedBuild/testReport/ and are all passing.