Fix most unit tests

Several unit tests were broken because of broken logic, not infrastructure
issues or edge cases. Fixed those to have a cleaner testing environment.

Removed most test from the allowed_failing_tests. The only survivors
are the ReqMgr tests which I can't figure out why they are broken in Jenkins only
and the REST tests which are broken locally too. Someone with more knowledge
of the REST stuff can fix those. Here is the breakdown of changes an explanations:

WMCore_t_ResourceControl_t_ResourceControl_t_ResourceControlTest_testInsertAllSE : New SiteDB emulator had a broken function.
WMComponent_t_RetryManager_t_RetryManager_t_RetryManagerTest_testA_Create : Create cooloff transitions to created instead of new
WMComponent_t_RetryManager_t_RetryManager_t_RetryManagerTest_testY_MultipleIterations : Create cooloff transitions to created instead of new
WMBS_t_WorkQueueTest_testWorkQueueService : Unit test was missing the creation of the BossAir schema
WMCore_t.WorkQueue_t.Policy_t.Start_t.Block_t.BlockTestCase.WMCore_t.WorkQueue_t.Policy_t.Start_t.Block_t.BlockTestCase.testWhiteBlackLists  : Unit test was broken after latest fixes
WMCore_t.WorkQueue_t.Policy_t.Start_t.ResubmitBlock_t.ResubmitBlockTest.WMCore_t.WorkQueue_t.Policy_t.Start_t.ResubmitBlock_t : All tests broken after SiteDB emulator change
WMCore_t.WorkQueue_t.Policy_t.Start_t.Dataset_t.DatasetTestCase.WMCore_t.WorkQueue_t.Policy_t.Start_t.Dataset_t.DatasetTestCase.testWhiteBlackLists : Tests were not properly resetting the defaults after every test.
WMCore_t.BossAir_t.GLiteLIParser_t.LoggingInfoParserTest.WMCore_t.BossAir_t.GLiteLIParser_t : Needed test files in a big commit with no apparent reason, restored them.
WMComponent_t.AlertGenerator_t.Pollers_t.Agent_t.AgentTest.WMComponent_t.AlertGenerator_t.Pollers_t.Agent_t.AgentTest.testComponentsPollerBasic : Can't assure no children condition in Jenkins
UserFileCache_t.UserFileCacheTest.UserFileCache_t.UserFileCacheTest.testChecksum : Needed test files in a big commit with no apparent reason, restored them.
WMCore_t.Services_t.WMStats_t.WMStats_t.WMStatsTest.WMCore_t.Services_t.WMStats_t.WMStats_t.WMStatsTest.testWMStatsWriter  : Change in response message broke unit test
WMCore_t.Storage_t.Plugins_t.DCCPFNALImpl_t.py : Test module and module-under-test are broken. Fixed imports only and added test to blacklist
WMCore_t.Storage_t.Plugins_t.SRMV2Impl_t.py : Test module and module-under-test are broken. Fixed imports only and added test to blacklist
WMCore_t.Services_t.pycurlFileUpload_t.py : Fixed updated imports and test functionality
WMCore_t.Services_t.DBS_t.DBSReader_t.DBSReaderTest.WMCore_t.Services_t.DBS_t.DBSReader_t.DBSReaderTest.testGetDBSSummaryInfo : Test was not marked properly as integration
WMCore_t.WMBS_t.JobSplitting_t.ParentlessMergeBySize_t.ParentlessMergeBySizeTest.WMCore_t.WMBS_t.JobSplitting_t.ParentlessMergeBySize_t.ParentlessMergeBySizeTest.testLocationMerging : Test was outdated compared to the setup method.
Merge pull request #4487 from dballesteros7/Clean-Up-UnitTests

Fix most unit tests