Add a "corosync ping" CLI command.

Add a "corosync ping" CLI command.

This patch adds a new CLI command to the res_corosync module.  It is primarily
used as a debugging tool.  It lets you fire off an event which will cause
res_corosync on other nodes in the cluster to place messages into the logger if
everything is working ok.  It verifies that the corosync communication is
working as expected.

I didn't put anything in the CHANGES file for this, because this module is new
in Asterisk 11.  There is already a generic "res_corosync new module" entry in
there so I figure that covers it just fine.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@370535 65c4cc65-6c06-0410-ace0-fbb531ad65f3