Adjust blocking scan during mount.

Scan operations can take minutes to complete, so we can't block the
delivery of onVolumeStateChanged(), as it has a pretty short
timeout on the system_server side.

Bug: 152005629
Test: atest MediaProviderClientTests:com.android.providers.media.client.LegacyProviderMigrationTest --rerun-until-failure 100
Change-Id: Ia5a5f5f128de2bc1fa2079a4642db7149559b7e1
1 file changed