build/make/Makefile: add a 'test_*' default target

allows 'make test_libvpx', etc. some reworking of the makefiles would be
needed to avoid hard coding targets here.

Change-Id: I18982dbf691e7d36ab8bcf5934bab9340687b061
(cherry picked from commit 25085a6ac21fc8e2341b92e2f1f14d5a7fef30c6)

build/make/Makefile

@@ -26,7 +26,7 @@ test-no-data-check:: .DEFAULT
 testdata:: .DEFAULT
 utiltest: .DEFAULT
 exampletest-no-data-check utiltest-no-data-check: .DEFAULT
-
+test_%: .DEFAULT ;
 
 # Note: md5sum is not installed on OS X, but openssl is. Openssl may not be
 # installed on cygwin, so we need to autodetect here.