Camera Wrapper: Only call cancel_auto_focus when the preview is enabled.

Change-Id: I2a26ba8bac3ef84f49ea5897cdeedbb5c0724e2b
msm8960-common: I don't want to see your face

Strengthen the prohibition against face detection as some third
party apps are ignoring it.

Change-Id: I88df1b40f27472b7ed40d745b4b5b59b6d2fa560