Add distribution unit checks for --force-full
Pulp 2.19 fixes a bug where distribution units for kickstart files were not synched on a --force-full.
Refactored ForceSyncTestCase for distribution units and any future type of unit to be tested with force-full with resync.
Added a test case to support checks on distribution units and make the test_sync.py test more extensible for other units using a tuple definition of the location and extension of the unit.
The rpm-kickstart is added to the fixtures for test. The fixture was derived from the Fedora 29 ISO and scaled down for test.