Allow hidden features in L to not fail the features CTS verifier test

Following features was added as hidden

android.hardware.hdmi.cec
android.software.leanback_only
android.software.voice_recognizers

So while this is not meant to be used by 3rd-party apps, it could be declared by devices

Bug: 17579748
Change-Id: I0324ad8d59811a4569842fae712875176f71805c