Do not return failure exit code (1) for unsupported testcases,
since it is expected for stable kernels.

Previously, ftracetest is expected to run only on current
release for avoiding regressions. However, nowadays we run
it on stable kernels. This means some test cases must return
unsupported result. In such case, we should NOT exit
ftracetest with error status for unsupported results so that
kselftest (upper tests wrapper) shows it passed correctly.

Note that we continue to treat unresolved results as failure,
if test writers would like to notice user that the test result
should be reviewed, they can use exit_unresolved.
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Steven Rostedt (VMware) <srostedt@goodmis.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>