Changes:
1. Moved directory voice_engine/include/mock to voice_engine/mock (current recommendation).
2. Updated includes where necessary.
Caution:
We need confirmation that these mocks are indeed used only locally.
R=kwiberg@webrtc.org
Review URL: https://webrtc-codereview.appspot.com/48089004
Cr-Commit-Position: refs/heads/master@{#9005}