tests: extend the AM_TESTS_ENVIRONMENT from check.mak
tests: extend the AM_TESTS_ENVIRONMENT from check.mak

To get the CK_DEFAULT_TIMEOUT defined for all tests

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

StreamUtils/gstreamer,centricular/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer