Prior to this commit, a properly configured Linux HVM would not
transition from the 'Transient' state to the 'Running' state according
to qvm-ls output, even if the HVM in question had the 'qrexec' feature
disabled.
This issue is caused by an unconditional qrexec check in the
'on_domain_is_fully_usable' method, and is resolved by adding
a check that short-circuits the qrexec check if the aforementioned
feature is not enabled for the VM in question.
2d55841a5e