added sleeps to the PluginTests hoping to help async logging
changed UnsubscribeFromSerialWhenNotRegistered_Test to use a random
available pool
added blockedByBug-924919 to
VerifyRedHatRepoFileIsPurgedOfBlankLinesByYumPlugin_Test
added blockedByBug-924919 to VerifyYumRepoListsEnabledContent_Test