tests: Use igt macros more

Often just folding together of the common if (cond) printf;
abort|igt_skip|igt_fail; pattern. But in a few cases I've ripped out
more since the igt macros will already print the condition and errno.

A few tests where more work (like ripping out return codes en masse)
is needed left as-is.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

tests/gem_hang.c

@@ -72,11 +72,9 @@ int main(int argc, char **argv)
 {
 	int fd;
 
-	if (argc != 2) {
-		fprintf(stderr, "usage: %s <disabled pipe number>\n",
-			argv[0]);
-		igt_fail(-1);
-	}
+	igt_assert_f(argc == 2,
+		     "usage: %s <disabled pipe number>\n",
+		     argv[0]);
 
 	bad_pipe = atoi(argv[1]);