Manage Excessive amount of spawned pids

rexi_utils:send uses the noconnect and nosuspend options to immediately
return to the controller and spawns new processes to send the messages, assuming
the remote node is only temporarily down. In the nosuspend case these pids
can hang around indefinitely and build up.

This patch sends the messages that need to be sent from spawned processes to a new
gen_server, rexi_governor, along with the caller pid. This pid is monitored and the
pids that it spawns are stored in a table. When the caller dies, the spawned pids
are killed.

BugzID: 15608
Some scaffolding for common test