rtla: Set distinctive exit value for failed tests

rtla: Set distinctive exit value for failed tests

A test is considered failed when a sample trace exceeds the threshold.
Failed tests return the same exit code as passed tests, requiring test
frameworks to determine the result by searching for "hit stop tracing"
in the output.

Assign a distinct exit code for failed tests to enable the use of shell
expressions and seamless integration with testing frameworks without the
need to parse output.

Add enum type for return value.

Update `make check`.

Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: John Kacur <jkacur@redhat.com>
Cc: "Luis Claudio R. Goncalves" <lgoncalv@redhat.com>
Cc: Eder Zulian <ezulian@redhat.com>
Cc: Dan Carpenter <dan.carpenter@linaro.org>
Cc: Jan Stancek <jstancek@redhat.com>
Link: https://lore.kernel.org/20250417185757.2194541-1-costa.shul@redhat.com
Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>
Reviewed-by: Tomas Glozar <tglozar@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>