ruby: set SenderMachine in messages of MOESI_CMP_directory

ruby: set SenderMachine in messages of MOESI_CMP_directory
This patch adds missing initializations of the SenderMachine field of
out_msg's when thery are created in the L2 cache controller of the
MOESI_CMP_directory coherence protocol. When an out_msg is created and this
field is left uninitialized, it is set to the default value MachineType_NUM.
This causes a panic in the MachineType_to_string function when gem5 is
executed with the Ruby debug flag on and it tries to print the message.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>