Address flake with volume change utilities

- Abstract methods which wait for async volume operations
- Modify cleanup/teardown to recover to known state which utility
  methods require
- Clean up redundant wrt @after state cleanup
- Modify testVolume to use new utilities to test
- Simplify silence test with new utilities

Test: atest AudioManagerTest --iterations=20
Bug: 293914397
Bug: 288333346
Change-Id: Ic6eedd7cac36d38c1092b34a033f59bceec4ec39
1 file changed