Ticket 47978: Deadlock between two MODs on the same entry between entry cache and backend lock
    
    Bug Description:
    	During a modify, the modified entry gets into the entry cache and is locked.
    	If after the be_txn_postop/txn_commit and before the modify returns
    	the modified entry gets out of the entry cache, the entry is not unlocked.
    	It can lead to hang as soon as an other write operation hit that unlocked entry.
    
    	This is a side effect of fix:
    		#47834 - Tombstone_to_glue: if parents are also converted to glue, the target entry's DN must be adjusted.
    
    Fix Description:
    	When the entry is locked, set a flag so that can later be unlocked
    	independently of its presence in the entry cache
    
    https://fedorahosted.org/389/ticket/47978
    
    Reviewed by: Noriko Hosoi (Thanks Noriko)
    
    Platforms tested: F22 (IPA CI test test_integration/test_vault.py, one failure out 2-4)
    
    Flag Day: no
    
    Doc impact: no
    
    (cherry picked from commit bdaed4e2fb4633d6fec16eb1ea55b7e2fcbd4df4)