Modified RAETChannel and Channel factory
Channel factory now has usage argument this is used by RAETChannel to determine routing destination addressing

Fixed three usages of RAETChannel

usage == 'local_cmd'  # Used by master_call for master to master communications
usage == 'call_cmd'   # Used by salt-call for cli to master communications through minion
otherwise default usage == None  # Used by minion to master communications

The destination estate is now None for all three usages.

These usages get translated into share destinations in the route dict for raet messages

usage 'local_cmd'  -> destination share 'local_cmd'
usage 'call_cmd'   -> destination share 'call_cmd'
usage None         -> destination share 'remote_cmd'

Fixed core.py Lane Router _process_uxd_rxmsg to recognize the share destinations and
do the apppropriate routing

Mainly this allows the destination estate to be none when a RAETCHannel is created and then
the router can substitute the approapriate destination estate for the master