Fix for potential level issue in Frequency tests

Added test and warning to let user know if level is not
set to max. This could happen if the device is in loudness
safety mode.
Refactored classess to share the level test logic.

Bug: 28431750
Change-Id: I26e5d3b34b0e9b7a02b0df4c69f39063a1f99b91
6 files changed