libvirt: test setting of CPU tuning data

The setting of the libvirt guest <cputune> data from the
flavor extra_specs quota parameter was never tested. In
fixing this omission, it was noticed that the data was
incorrectly passed around as a string instead of an int.

Change-Id: Ie8b31feddf6c546eb05ca00ead5c56bcd535dd84
Merge "libvirt: test setting of CPU tuning data"