#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
Client timeouts work on the last_cap_renew time on a session -- CLIENT_CAPRELEASE and CLIENT_CAPS messages don't plink that field as far as I can see, so this shouldn't affect timeouts.