ceph_key: fix rstrip for python 3

Removing bytes literals since rstrip only supports type String or None.

Signed-off-by: Sébastien Han <seb@redhat.com>
(cherry picked from commit f5c2ca3710)

library/ceph_key.py

@@ -678,8 +678,8 @@ def run_module():
         end=str(endd),
         delta=str(delta),
         rc=rc,
-        stdout=out.rstrip(b"\r\n"),
-        stderr=err.rstrip(b"\r\n"),
+        stdout=out.rstrip("\r\n"),
+        stderr=err.rstrip("\r\n"),
         changed=True,
     )