kbfs_ops_concur_test: extend the retry/error sync test to SyncAll
kbfs_ops_concur_test: extend the retry/error sync test to SyncAll

Issue: KBFS-2069

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