tests: use igt_fail instead of exit(param != 0)

Mostly a sed job with too manual fixups:
- one case of using _exit instead of exit
- and one case which under some conditions use 77, so convert that
  check to an igt_skip.

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

tests/gem_cs_prefetch.c

@@ -102,7 +102,7 @@ int main(int argc, char **argv)
 	bufmgr = drm_intel_bufmgr_gem_init(fd, 4096);
 	if (!bufmgr) {
 		fprintf(stderr, "failed to init libdrm\n");
-		exit(-1);
+		igt_fail(-1);
 	}
 
 	drm_intel_bufmgr_gem_enable_reuse(bufmgr);