DO NOT MERGE: Limit tests to Rust and one representative other

.murdock

@@ -187,7 +187,7 @@ _greplist() {
 # get list of all app directories
 get_apps() {
     make -f makefiles/app_dirs.inc.mk info-applications \
-        | $(_greplist $APPS) | sort
+        | $(_greplist $APPS) | sort | grep rust\\\|xfa\\\|kconfig
 }
 
 # take app dir as parameter, print all boards that are supported