Switch Gallery to Gallery2 app for emulator images

Change gallery application from Gallery to Gallery2. Gallery does not
seem to have been changed in a long time and AOSP images for devices use
Gallery2 so emulator images should match that.

BUG: 29334386
Change-Id: I1054af38aa1c100cdb671688e2d7aaaf882753af
(cherry picked from commit ea9467cd003f51e83e497b6fbd1a4abd9705be29)