basemixer: Add basic test

Change-Id: Iab0a66e7a90bc72068fe5e89707e4cb032da57e4
basemixer: Add action to add ports handled by the mixer

Change-Id: Ifeed659ac7306f9f8d91c22a1358bbfe542b11c2
basemixer: Change parent class

Change-Id: I8d49f869da9bf2102d075b1367d4144bc6873602