Add audiosystem unit tests

Also moved common code to audio_test_utils.cpp

Bug: 215794103
Test: atest audiorecord_tests audiotrack_tests \
 audiorouting_tests trackplayerbase_tests audiosystem_tests

Merged-In: I939e2d9f7cd5b55b7255f9f497cd33b2e129b3ff
Change-Id: I939e2d9f7cd5b55b7255f9f497cd33b2e129b3ff
8 files changed