Port 5a39e777089d8bde6d0a620830a898c1cf3dd924 ("events: add support for
wildcard event handlers") from qubes-core-admin:
Support registering handlers for more flexible wildcard events: not only
'*', but also 'something*'. This allows to register handlers for
'property-set:*' and such.
This is especially the case for domain-shutdown event for DispVM - when
handled, DispVM can be already removed. Give the handled VM object even
if actual VM is already removed. For this, avoid VM existence check by
using domains.get_blind() method.
And actually implement domains.get_blind() method - it was present only
in generic collection, but not VMCollection.
Empty parameter value is encoded as b'parameter\0\0', so we can't simply
read the data until b'\0\0', because it isn't necessary event end.
Instead, read event parts separately, according to specification.
