tests: roll out igt_simple_init/igt_simple_main

Also use igt_skip a bit more to simplify some of the tests.

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

tests/core_getclient.c

@@ -32,7 +32,7 @@
 /**
  * Checks DRM_IOCTL_GET_CLIENT.
  */
-int main(int argc, char **argv)
+igt_simple_main
 {
 	int fd, ret;
 	drm_client_t client;
@@ -57,5 +57,4 @@ int main(int argc, char **argv)
 	igt_assert(ret == -1 && errno == EINVAL);
 
 	close(fd);
-	return 0;
 }