perf test shell lock_contention: Extra debug diagnostics

perf test shell lock_contention: Extra debug diagnostics

In test_record_concurrent, as stderr is sent to /dev/null, error
messages are hidden. Change this to gather the error messages and dump
them on failure.

Some minor sh->bash changes to add some more diagnostics in
trap_cleanup.

Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Athira Rajeev <atrajeev@linux.ibm.com>
Cc: Blake Jones <blakejones@google.com>
Cc: Chun-Tse Shao <ctshao@google.com>
Cc: Collin Funk <collin.funk1@gmail.com>
Cc: Howard Chu <howardchu95@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Polensky <japo@linux.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Li Huafei <lihuafei1@huawei.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Nam Cao <namcao@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steinar H. Gunderson <sesse@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20250821163820.1132977-5-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>