Reinitialize hardware renderer after eglTerminate()

Bug #8066455

ViewRootImpl was properly detecting that the renderer was not
ready to draw but would simply schedule another frame, thus sending
the systemui into an inifite redraw loop. This change reinitializes
the renderer if needed (if the renderer is requested but not enabled.)

This CL also fixes an issue caused by the default wallpaper. Since it
never calls eglTerminate(), managed contexts are never reclaimed.

Change-Id: Idb8caa672be8ee35f6e6a7e942d9abd8aa100967