We can't just update the state of the connector and CRTC from KMS since
it might contain too new updates, e.g. from a from a future hot plug. In
order to not add ad-hoc hot plug detection everywhere, predict the state
changes by looking inside the MetaKmsUpdate object, and let the hot-plug
state changes happen after the actual hot-plug event.

This fixes issues where connectors were discovered as disconnected while
doing a mode-set, meaning assumptions about the connectedness of
monitors elsewhere were broken until the hot plug event was processed.

Fixes: #782

!826