kselftest/tty: Report a consistent test name for the one test we run

kselftest/tty: Report a consistent test name for the one test we run

Currently the tty_tstamp_update test reports a different exit message
for every path it can exit via. This can be confusing for automated systems
as the string that gets logged is interpreted as a test name so if the test
status changes they can't tell that it's the same test case that was run,
they can see that the overall status of the test program is a failure but
it's not clear that it was running the same test.

Change all the messages that are logged to be diagnostic prints and log the
name of the program as the test name.

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>