Add Wear keycodes to emulator key layout file.

The SLEEP keycode is used by Android Wear to indicate a
"palming" gesture (covering the screen with one's hand).

The STEM_* buttons are used for side buttons on Wear.

The keycode values were added to the emulator in
http://r.android.com/330771

Bug: 19996432
Change-Id: Ib90c3b27209b0059ebc1c2cce46cc732a677d557