retry group_recvmsg() if it returned None (even though nonblocking is false)

git-svn-id: svn://bind10.isc.org/svn/bind10/trunk@1446 e5f2f494-b856-4b98-b285-d166d9295462

src/bin/cmdctl/cmdctl.py.in

@@ -299,6 +299,8 @@ class CommandControl():
             seq = self.cc.group_sendmsg(msg, module_name)
             #TODO, it may be blocked, msqg need to add a new interface waiting in timeout.
             answer, env = self.cc.group_recvmsg(False, seq)
+            while answer == None:
+                answer, env = self.cc.group_recvmsg(False, seq)
             if answer:
                 try:
                     rcode, arg = isc.config.ccsession.parse_answer(answer)