xbps-src: add make_check_pre

$make_check_pre can be used for wrapper commands like xvfb-run or
dbus-run-session which are common ways to make tests work. This way many
templates can avoid defining their own do_check function.

common/build-style/python-module.sh

@@ -49,7 +49,7 @@ do_check() {
 			fi
 		fi
 
-		python${pyver} setup.py ${make_check_target:-test} ${make_check_args}
+		${make_check_pre} python${pyver} setup.py ${make_check_target:-test} ${make_check_args}
 		rm build
 	done
 }