tests: Add blob-property test

Exercises the new blob-creation ioctl, testing lifetimes and behaviour
of user-created blobs, as well as exercising all the invariant
conditions we guarantee from modes exposed as blob properties.

v2: Renamed to core_prop_blob, skip test if blob not available.
v3: No changes.
v4: Consistently return 0/errno.
v5: Use do_ioctl_err and igt_assert_fd.
    Use igt_assert_*() helper macros rather than direct igt_assert().

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Daniel Vetter <daniel.vetter@intel.com>

tests/.gitignore

@@ -3,6 +3,7 @@ core_get_client_auth
 core_getclient
 core_getstats
 core_getversion
+core_prop_blob
 drm_auth
 drm_import_export
 drm_read