FIX: replaced threading.RLock with LockRing
FIX: removed "from DIRAC.Core.Utilities.DictCache import *" from
DIRAC.Core.Utilities.__init__ and redone all import paths to be working
again.
Merge pull request #1378 from ubeda/DictCacheWithLockRing

[v6r7]FIX: replaced threading.RLock with LockRing