rtla/tests: Check rtla output with grep

rtla/tests: Check rtla output with grep

Add argument to the check command in the test suite that takes a regular
expression that the output of rtla command is checked against. This
allows testing for specific information in rtla output in addition
to checking the return value.

Two minor improvements are included: running rtla with "eval" so that
arguments with spaces can be passed to it via shell quotations, and
the stdout of pushd and popd is suppressed to clean up the test output.

Cc: John Kacur <jkacur@redhat.com>
Cc: Luis Goncalves <lgoncalv@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Chang Yin <cyin@redhat.com>
Cc: Costa Shulyupin <costa.shul@redhat.com>
Cc: Crystal Wood <crwood@redhat.com>
Cc: Gabriele Monaco <gmonaco@redhat.com>
Link: https://lore.kernel.org/20250626123405.1496931-7-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>