Add mediaStore.waitForIdle before scans

Attempt to reduce flakiness by adding MediaStore.waitForIdle.

Bug: 188981504
Bug: 191845116
Test: atest ModernMediaScannerTest
Change-Id: Idd8250a9f118dd1051611a1e4f2172a1539dccab
Merged-In: Idd8250a9f118dd1051611a1e4f2172a1539dccab
(cherry picked from commit f0dbbe53c4c5d270b10c540668b5cacda2f40b77)
1 file changed