perf tests shell: Skip base_* dirs in test script search

perf tests shell: Skip base_* dirs in test script search

The test scripts in base_* directories currently have their own drivers
that run them. Before this patch, the shell test-suite generator causes
them to run twice. Fix that by skipping them in the generator.

A cleaner solution (for future) will be to use the directory structure
idea (introduced by Carsten Haitzler in 7391db645938 ("perf test:
Refactor shell tests allowing subdirs")) to generate test entries with
subtests, like:

  $ perf test list
  [...]
  97: perf probe shell tests
  97:1: perf probe basic functionality
  97:2: perf probe tests with arguments
  97:3: perf probe invalid options handling
  [...]

There is already a lot of shell test scripts and many are about to come,
so there is a need for some hierarchy.

Signed-off-by: Michael Petlan <mpetlan@redhat.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240702110849.31904-3-vmolnaro@redhat.com
Signed-off-by: Veronika Molnarova <vmolnaro@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>