FIX: CLO-4807 exception when unregistering JDBC driver on JBoss

git-svn-id: https://svn.javlin.eu/svn/cloveretl.opensource/trunk-3-5@16393 a09ad3ba-1a0f-0410-b1b9-c67202f10d70
MINOR: comment fixed

git-svn-id: https://svn.javlin.eu/svn/cloveretl.opensource/trunk-3-5@16395 a09ad3ba-1a0f-0410-b1b9-c67202f10d70
UPDATE: do not free cached JDBC drivers from engine

git-svn-id: https://svn.javlin.eu/svn/cloveretl.opensource/trunk-3-5@16398 a09ad3ba-1a0f-0410-b1b9-c67202f10d70