Testunitready

Here are two patches that :

1, adds support for commands that do not need/use unmarshalling
2, adds support for testunitready

btw,   did 42c78bf2a2d63f break enums?
test_inquiry.py has a problem looking up VPD pages

I think the problem is that if we try to lookup a value that does not exist, then we get a python failure.
For example in scsi_cdb_inquiry.py we only know about a subset of VPD pages that we define in
vpds = ...
I have a crazy device that reports vpd pages that does not exist and then when we try to lookup the nonexistent vpd page in
pg == 31
print '%02x: %s' % (pg, INQUIRY.VPD[pg])
python aborts.

For this case I think the enum should probably return "<unknown>" or something instead.