Adds a test_format database column and a value in the API return for the
test format version, starting at 0 for the existing format as of 0.9.37.
References #143
Allow a VM to specify its migration type as a default choice. The valid
options are "default" (i.e. behave as now), "live" which forces a live
migration only, and "shutdown" which forces a shutdown migration only.
The new option is treated as a VM meta option and is set to default if
not found.