1) Introduce new exception type XendInvalidDomain that maps to the high level

1) Introduce new exception type XendInvalidDomain that maps to the high level
   XEND_INVALID_DOMAIN faultType.
2) Fix exception logic in XMLRPCServer
3) Fix TCP server
4) Remove catching of ProtocolError in main.py.  ProtocolErrors only occur
   when there is an exception in the exception handling code which shouldn't
   ever happen.  I've reproduced the error cases described by Ewan with
   xend_domain_setTargetMemory and once I fixed the exception logic, I get a
   normal faultType of 1 as would be expected.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>