Improve handling of crashing a11y services.

We were confusing handling of services that were unbound with
those that had crashed. We would lose track of services that
has crashed, start new ones, and then when the system restarted
a killed services we would have multiple instances running. It
was possible for this to get very out of hand.

Bug: 30306689
Change-Id: I4e63d25b6d2fec3ec68f450a4602898c43a2b2ad