monclient: use blank fsid (instead of epoch==0) for monmap checks
monclient: use blank fsid (instead of epoch==0) for monmap checks

We can safely mkfs with an epoch=0 monmap as long as the fsid is set.  And
that is what commit f31825cee5300c708800a01a08201eef2bc03c0c changed.

Instead, use a zeroed fsid to tell if the monmap is valid/usable.

Signed-off-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@newdream.net>

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph