lib: detect AUM crash

If AUM is crashed by any reason (SIGSEGV for example) the function
`apply_update_sync` don't detect that behavior and exit with error code
after timeout (~8 min). This is leading to false positive result if we
are expecting the update failure.

Added the check of AUM restart by systemd and return code `99` for that case.
Different error code allow to determine if the upgrade is failed as
expected or we have bug in AUM code. Reduces the test time in case of
AUM crash.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>