Use fabric for shard #db{} records

Fixes _info calls on clustered views.

closes COUCHDB-2461
diff --git a/src/couch_index_server.erl b/src/couch_index_server.erl
index 8fe4b18..76adb6a 100644
--- a/src/couch_index_server.erl
+++ b/src/couch_index_server.erl
@@ -63,7 +63,9 @@
     lists:foldl(ValidateFun, ok, EnabledIndexers).
 
 
-get_index(Module, <<"shards/", _/binary>>=DbName, DDoc) ->
+get_index(Module, #db{name = <<"shards/", _/binary>> = DbName}, DDoc) ->
+    get_index(Module, DbName, DDoc);
+get_index(Module, <<"shards/", _/binary>> = DbName, DDoc) ->
     {Pid, Ref} = spawn_monitor(fun() ->
         exit(fabric:open_doc(mem3:dbname(DbName), DDoc, [ejson_body]))
     end),