#7317 ENOSPC and OSD epoch barrier handling


Related:
https://github.com/ceph/ceph-qa-suite/pull/225
https://github.com/ceph/ceph-client/pull/7
Ah, actually it's in there because the ldout prefix in this file looks for a local called `whoami` -- added comment to that effect.  Bit hacky but better than not having the debug output available