Implemented EZP-20288: As a support engineer I would like eZDB & eZFS2 Cluster removed in favor of eZDFS
Merge branch 'EZP-20288'

Conflicts:
	doc/bc/5.1/changes-5.1.txt
	kernel/classes/clusterfilehandlers/dbbackends/mysqli.php
	kernel/classes/clusterfilehandlers/ezdbfilehandler.php
	kernel/clustering/dbmysqli.php
	kernel/private/classes/clusterfilehandlers/ezfs2filehandler.php
	tests/tests/kernel/classes/clusterfilehandlers/ezdbclusterstalecache_test.php
	tests/tests/kernel/classes/clusterfilehandlers/ezdbfilehandler_test.php
	tests/tests/kernel/classes/clusterfilehandlers/ezfs2clusterstalecache_test.php
	tests/tests/kernel/classes/clusterfilehandlers/ezfs2filehandler_test.php