rgw: drop async pool create completion reference

Fixes: ceph#6444
Backport: dumpling
If pool creation fails (e.g., due to -EEXIST) then we leak the
completion object. Earlier we couldn't just drop the reference, as
librados have already removed the internal completion object. This fix
drop the completion reference even if got an error, which is now
possible.

Signed-off-by: Yehuda Sadeh <[email protected]>

src/rgw/rgw_rados.cc

@@ -2182,8 +2182,8 @@ int RGWRados::create_pools(vector<string>& names, vector<int>& retcodes)
       if (r < 0) {
         ldout(cct, 0) << "WARNING: async pool_create returned " << r << dendl;
       }
-      c->release();
     }
+    c->release();
     retcodes.push_back(r);
   }
   return 0;