tests: Don't silently ignore test errors

When there was a test error, such as a shell command failure, the
function used for the ERR trap, error_handler(), was causing the error
to be silently ignored by the test runner.

It was calling exit_handler() directly, before calling fatalerror().
This caused $_fatal to be left unset when exit_handler() was called.
exit_handler() sources epilogue.inc and the last bit of epilogue.inc
exits with $num_testfailures if $_fatal was unset. The fatalerror() call
site in error_hanlder() was never reached. So, as long as there were no
test failures, then an error in a test script would cause the test to
exit early with 0.

It is safe to simply call fatalerror() from error_handler() because
fatalerror() sets $_fatal to true and exits. This causes exit_handler()
to be called and since $_fatal is set to true, prologue.inc exits with
127.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Steve Beattie <steve@nxnw.org>

tests/regression/apparmor/prologue.inc

@@ -89,9 +89,6 @@ testfailed()
 
 error_handler()
 {
-	#invoke exit_handler to cleanup
-	exit_handler
-
 	fatalerror "Unexpected shell error. Run with -x to debug"
 }