MediaSession2: Fix bug in runtest.sh for finding test apk

The script had searched the apk under the ${OUT}, but it sometimes match
with the invalid apk under ${OUT}/obj/PACKAGING.

Limits the search directory to ${OUT}/system and ${OUT}/data to exclude
obj directory.

Test: Run all MediaComponents tests once
Change-Id: I733b381cbc8e56b5c28515bc93931ce1e5d67e40