It's been a while since the "Test ID RFC" came out:

https://www.redhat.com/archives/avocado-devel/2016-March/msg00024.html

Still, we've been referring to test URLs all around our code
and also on user visible strings.  This is an attempt to rename
the mentions of "URLs" that really should be "test references"
or simply "references" at this point.
Signed-off-by: NCleber Rosa <crosa@redhat.com>