Turn on the instrumentation by default for the java code in APEXes

Bug: 149353192
Test:  DIST_DIR=dist_dir TARGET_BUILD_VARIANT=userdebug
EMMA_INSTRUMENT=true NATIVE_COVERAGE=true
TARGET_BUILD_APPS="com.android.media"
vendor/google/build/build_unbundled_coverage_mainline_module.sh and
check that jacoco-report-classes.jar is created.
Change-Id: I28e3dc82b7913f60b2278126fca255306e48a424