change executor match from equality check to regex (re.fullmatch)

[shahzebsiddiqui]

There was an issue with validating test when executor property was using a regex. Current behavior was equality check with the executors defined in configuration file. This caused tests like https://github.com/buildtesters/buildtest-nersc/blob/devel/buildspecs/apps/hpctoolkit/hpctoolkit_cuda_vecadd_pc_perlmutter.yml to fail where we had the following for executor - executor: '(perlmutter|muller).slurm.regular'

With this change i was able to confirm validation and tags was picking up executors.

(buildtest)  ~/gitrepos/buildtest-nersc/ [devel] buildtest bc find --filter buildspec=/global/u1/s/siddiq90/gitrepos/buildtest-nersc/buildspecs/apps/hpctoolkit/hpctoolkit_cuda_vecadd_perlmutter.yml
          Buildspec Cache: /global/u1/s/siddiq90/gitrepos/buildtest/var/buildspecs/cache.json
 name            ┃ type   ┃ executor                          ┃ tags ┃ description
━━━━━━━━━━━━━━━━━╇━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 hpctoolkit_cuda │ script │ (perlmutter|muller).slurm.regular │ e4s  │ HPCToolkit vector add CUDA test

@wyphan with this change i expect hpctoolkit test will run now that we change executor check to re.fullmatch