osd: block requests on object during COPY_FROM

Block any request on an object (read or write) during the COPY_FROM
operation.

This could potentially be broken down into read vs write operations without
much difficulty, but blocking any op indescriminately is sufficient for
now, so let's keep it simple.

Signed-off-by: Sage Weil <sage@inktank.com>
ceph_test_rados: use get_version64() throughout

Signed-off-by: Sage Weil <sage@inktank.com>
ceph_test_rados: submit a racing read with every COPY_FROM

Verify that the racing read completes after the COPY_FROM does (i.e., is
blocked by it).

Signed-off-by: Sage Weil <sage@inktank.com>
osd: allow a copy_from without knowing the src_version

If we don't spcify the version up front, learn the version after the first
chunk and enforce it thereafter to ensure we do not torn content.

Signed-off-by: Sage Weil <sage@inktank.com>
fix ceph-test-rados