Delay auto key frame insertion in realtime configuration

Whe auto keyframe insertion is enabled and conditions are right (scene change)
the encoder can decide to insert a key frame and does a re-encoding. This can
introduce extra latency. In RT mode we do not do the re-encoding of the current
frame but force the next frame to key frame.

Change-Id: I15c175fa845ac4c1a1f18bea3676e154669522a7