scripts/run-tests.sh: Use the filter flag values when listing tests

Testcase:
scripts/run-tests.sh -l -T fast-feedback.testlist -x vgem_basic

Previously the filters (-T for testlist, -t/-x for regex
include/exclude) were silently dropped when listing tests. Actually
use them for listing, since that works properly when using igt_runner.

Warning for those using piglit (the -p flag): The -x flag for listing
with piglit is the same as -t at this time:
mesa/piglit#29



v2: Remember to git add after removing debug echos instead of breaking CI

Signed-off-by: Petri Latvala <petri.latvala@intel.com>
Cc: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Cc: Tomi Sarvela <tomi.p.sarvela@intel.com>
Reviewed-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>