selftests: ftrace: Add --fail-unsupported option

Add --fail-unsupported option to fail the test result if
ftracetest gets UNSUPPORTED result. UNSUPPORTED usually
happens when the kernel is old (e.g. stable tree) or some
kernel feature is disabled.

However, if newer kernel has any bug or regression, it
can make test results in UNSUPPORTED too. This option
can detect such kernel regression.

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>