Abandon in-flight app-search session when user stops

This is an attempt to fix an issue observed in automation test where
when user is stopeed immediately after it started, ShortcutManager is
still processing the unlock event which eventually leads to error in
creating folder for a stopped user in icing.

Bug: 183618378
Test: To be verified in TreeHugger
Change-Id: I7ae541edc0b9724b8dc7885b70f4f754c2e6da2c