`-n` and `-x` are not combined correctly

[vkarak]

Combining the -n and trying to exclude a test using the -x it has no effect. How to reproduce:

./bin/reframe -C config/machines.py -c tutorials/cscs-webinar-2022/tests/stream9.py -n stream_scale_test -x /5ccda674 -l

- stream_scale_test %threading=4 %stream_binaries.elem_type=float /5ccda674
    ^stream_build %elem_type=float ~tresa:default+gnu /bed1cb01
- stream_scale_test %threading=2 %stream_binaries.elem_type=float /a02e1a74
    ^stream_build %elem_type=float ~tresa:default+gnu /bed1cb01
- stream_scale_test %threading=1 %stream_binaries.elem_type=float /a54fb2dd
    ^stream_build %elem_type=float ~tresa:default+gnu /bed1cb01
- stream_scale_test %threading=4 %stream_binaries.elem_type=double /986c1e0b
    ^stream_build %elem_type=double ~tresa:default+gnu /3d9fd09f
- stream_scale_test %threading=2 %stream_binaries.elem_type=double /d976421a
    ^stream_build %elem_type=double ~tresa:default+gnu /3d9fd09f
- stream_scale_test %threading=1 %stream_binaries.elem_type=double /b7f1a81d
    ^stream_build %elem_type=double ~tresa:default+gnu /3d9fd09f

Although the stream_scale_test is selected, but the test with threading=4 (5ccda674) is still selected.