Stop XAPI running if we're not in dom0.

Fixes issue 438 (original issue) by preventing XAPI from running
if we're not in dom0, i.e. we're in a nested Xen environment and
we have not yet rebooted.
Merge pull request #61 from BobBall/issue-438

Stop XAPI running if we're not in dom0.
Block xapi waiting for xenopsd-xc

Second fix for issue 438
Merge pull request #62 from BobBall/issue-438

Block xapi waiting for xenopsd-xc
Remove unused check_output import
Merge pull request #63 from BobBall/issue-438

Remove unused check_output import