r24773: Fix a ctdb connection lockup

r24773: Fix a ctdb connection lockup

The lockup could happen when packet_read_sync() gets two packets in a row, the
first one being an async message, and the second one being the response to a
ctdb request.

Also add some debug msg to ctdb_conn.c, and cut off the "locking key" messages
to only dump 20 hex chars at debug level 10. >10 will dump everything.
(This used to be commit 0a55880a240b619810371a19144dd0a75208adfe)