check.mak: set CK_DEFAULT_TIMEOUT for all tests

Set it as part of the AM_TESTS_ENVIRONMENT variable so that it
is the same when running make-check from the top-level dir or
when running the element.check variations

https://bugzilla.gnome.org/show_bug.cgi?id=761472

check.mak

@@ -12,36 +12,32 @@ check-valgrind:
 endif
 
 LOOPS ?= 10
+AM_TESTS_ENVIRONMENT = CK_DEFAULT_TIMEOUT=20
 
 # run any given test by running make test.check
 # if the test fails, run it again at at least debug level 2
 %.check: %
 	@$(AM_TESTS_ENVIRONMENT)					\
-	CK_DEFAULT_TIMEOUT=20					\
 	$* ||							\
 	$(AM_TESTS_ENVIRONMENT)					\
 	GST_DEBUG=$$GST_DEBUG,*:2				\
-	CK_DEFAULT_TIMEOUT=20					\
 	$*
 
 # just like 'check', but don't run it again if it fails (useful for debugging)
 %.check-norepeat: %
 	@$(AM_TESTS_ENVIRONMENT)					\
-	CK_DEFAULT_TIMEOUT=20					\
 	$*
 
 # run any given test in a loop
 %.torture: %
 	@for i in `seq 1 $(LOOPS)`; do				\
 	$(AM_TESTS_ENVIRONMENT)					\
-	CK_DEFAULT_TIMEOUT=20					\
 	$*; done
 
 # run any given test in an infinite loop
 %.forever: %
 	@while true; do						\
 	$(AM_TESTS_ENVIRONMENT)					\
-	CK_DEFAULT_TIMEOUT=20					\
 	$* || break; done
 
 # valgrind any given test by running make test.valgrind