tests: rename env vars for tests

Rename WAYLAND_TESTS_NO_TIMEOUTS to WAYLAND_TEST_NO_TIMEOUTS.
Further rename NO_ASSERT_LEAK_CHECK to WAYLAND_TEST_NO_LEAK_CHECK.
Now the naming is consistent not only here, in Wayland, but even with
naming of weston env varibles related to testing.

This is version 2 of the patch. The first version just renamed
NO_ASSERT_LEAK_CHECK to WAYLAND_TEST_NO_LEAK_CHECK.

Signed-off-by: Marek Chalupa <mchqwerty@gmail.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Acked-by: Bryce Harrington <b.harrington@samsung.com>