Seeing a log message saying 'flags=93' is ambiguous & confusing unless
you happen to know that libvirt always prints flags as hex.  Change our
debug messages so that they always add a '0x' prefix when printing flags,
and '0' prefix when printing mode. A few other misc places gain a '0x'
prefix in error messages too.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>