Bug Description: if a thread holding the connection monitor
		 is stuck in polling and the client doesn't
		 respond, the main thread can be blocked on
		 this connection when iterating the connection
		 table.

Fix Description: Implement a test and enter function for the connection
		 monitor, so the main thread will never wait for a
		 connection monitor already owned by an other thread

https://fedorahosted.org/389/ticket/48882

Reviewed by: Noriko, Thanks

(cherry picked from commit 7110db91e75f392f1c83643d9aa88895992d9c01)
(cherry picked from commit 19c4638f689e88ebc1eaec030039d2a4521aa7c4)