Some of the LXC callbacks did not lock the virDomainObjPtr
instance. This caused transient errors like

error: Failed to start domain busy-mount
error: cannot rename file '/var/run/libvirt/lxc/busy-mount.xml.new' as '/var/run/libvirt/lxc/busy-mount.xml': No such file or directory

as 2 threads tried to update the status file concurrently
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>