Added back the recents button to activity over lockscreen

When recents button is pressed, check if keyguard is up and then wait
for dismiss before going to recents. Forces only the back button to be
shown when bouncer is shown.

Fixes: ag/63879974
Test: open maps, navigate, turn off screen then back on
Change-Id: Ia7cec13af5bad261a9eb187df57fe62a5f96326e