Improve orphan transaction logging

This patch improves logging when we perform last-resort cleanup
from garbage collector, so that the type of client handle is also
logged. This allows us to discern snapshots and snapshots.

Also lower the logging level to INFO, as this is something that
should be fixed by whoever is causing it, but it does not pose
serious threat to stability.

Change-Id: Iad55c49de87ca73f9671f04f569be7eae0e4f885
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>