Many functions and especially standalone tools takes the lock itself, so
to prevent deadlocks, as a rule execute the tests with lock released.
Also reload qubes.xml before cleanup.
The statement that unlock_db() is always called directly after save() is
no longer true - tests holds the lock all the time, doing multiple saves
in the middle.
This is to make sure that QubesVmCollection state is consistent with
qubes.xml - unfortunately some changes are applied to Qubes*Vm object
only at load time (for example connected_vms collections).
Test suite now logs to three places:
* syslog
* ${HOME}/qubes-tests.log
* /dev/kmsg (only start and errors; this is handy while debugging Oopses by
correlating them with tests)
