Use test tags for skipping tests
Use test tags for skipping tests

This loads all individual test functions from the suite and checks
the tags to decide whether the test should be skippend or not.
We are abusing some unittest internal API to do this, but all
private functions works with Python 2 and Python 3 and general
looks like "stable enough" API.

rhinstaller/libblockdev,rhinstaller/libblockdev,rhinstaller/libblockdev