compositor-drm: Exit if we failed to get drm master
compositor-drm: Exit if we failed to get drm master

We can do anything without drm master.  Also log an error in case we
fail to drop it, which will be trouble for whoever we're switching to.

eyolfson/weston,mchalupa/weston,jonnylamb/weston,krezovic/weston,jonnylamb/weston,Gnurou/weston,krezovic/weston,giucam/weston,mchalupa/weston,giucam/weston,Fantu/compositor-spice,Tarnyko/weston-xdg_surface_present,Fantu/compositor-spice,Fantu/compositor-spice,sir-murray/weston,Gnurou/weston,udoprog/weston,udoprog/weston,xorgy/weston,xorgy/weston,kwm81/weston,eyolfson/weston,sir-murray/weston,kwm81/weston,Tarnyko/weston-xdg_surface_present