Miscellaneous fixes to SoundPool unit test

Explicitly specify API level 8, to permit same .apk be used with multiple platform versions.
In the priority test, use different samples for low and priority sounds,
    so it is possible to hear the difference.
Increase sleep times to make it easier to hear.
Only use Log.e for errors.
Add more logs and sleeps.
Pan more slowly.
Fix typos in logs about the test names.
Fix typo in pan comment.

Change-Id: Iebce07ca0cf3d6fa1b04faa8577faa1c6d25f8e6