Pass EXCLUDE_FROM_RECENTS when starting secure camera.

Camera started from the secure lock screen does not
show all the pictures in the camera roll. If users
launch camera from recent apps, they may enter secure
camera mode accidentally. Pass EXCLUDE_FROM_RECENTS
flag to prevent this.

bug:7053266
Change-Id: I0ad526d919dac02f358b25493777d7d73da6987f