Fix test_validate to run by itself

Resources were not initialized, so all tests would fail. Calls the same
method which is called internally to load all plugins.

Change-Id: I696f1d40499bb9a3ca6fde5d08101e9ddabc4369
Depend on discover to fix python2.6 tests

It also fix a failure introduced by using 2.7-specific setUpClass.

Fixes: bug #1175753
Change-Id: I63ba61050602df92c654bd70519947965494df37
Merge "Depend on discover to fix python2.6 tests"
Merge "Fix test_validate to run by itself"