test_stallers: new calls to config.MDOps() should see the staller
test_stallers: new calls to config.MDOps() should see the staller

This didn't matter before because previously callers use
jServer.delegateMDOps directly.

Issue: KBFS-1590

keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs