* fixes-20170929:
vm: do not start QubesDB watch instance multiple times
vm: report storage.stop() errors to log
vm: move comment
storage: fix method name in LinuxModules volume
Prevent removing domain that is referenced from anywhere
vm: add vm.klass property
Move QubesVM.{name,qid,uuid,label} to BaseVM
vm: do not allow deleting template property from AppVM and DispVM
vm/qubesvm: emit event on failed startup
vm/qubesvm: remove duplicated qmemman_client.close()
vm/dispvm: cleanup DispVM also on failed startup
vm/dispvm: fix error message
ext/block: properly list devtype=cdrom option
block: fix handling non-existing devices
block: improve handling device name and description