Destroy idle VMs after some period of time

NOTE: If you have an existing database, you need to discard the TTL
index; the easiest way is to drop the 'sessionmodels' collection.

Fixed issue with proxy sockets that sometimes caused client socket
to stay open when it should close.
Changed how proxy handles and removes sessions (no longer uses
MongoDB TTL index).
Now session 'lastAction' state is used to determine VM idle time.
Added interval to terminate expired VMs (those that have been idle
for too long), remove the associated session, and remove the user's
VM information.
Fixed whitespace formatting of openstack module.