osd/ReplicatedPG: stage object chunks to replicas during COPY_FROM

As we get each chunk of data during the COPY_FROM operation, write it out
to a temporary object on the replicas.  When we get all the pieces, move
it into place.

Signed-off-by: Sage Weil <sage@inktank.com>
ceph_test_rados: more readable output

Signed-off-by: Sage Weil <sage@inktank.com>
osd/ReplicatedPG: factor some bits into finish_copy

This is a bit cleaner and hopefully more usable for osd-driven cache
promotion.

Signed-off-by: Sage Weil <sage@inktank.com>
osd: add infrastructure to block io on an obc

Add an is_blocked() method for the obc, and add infrastructure to block
any operations if it returns true.  Clean up on_change(), and add a helper
to kick an obc when whatever condition leading to it being blocked is no
longer true.

For now, is_blocked() is always false...

Signed-off-by: Sage Weil <sage@inktank.com>
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 specify the version up front, learn the version after the first
chunk and enforce it thereafter to ensure we do not get torn content.

Signed-off-by: Sage Weil <sage@inktank.com>
librados: test copy_from without src_version specified

Signed-off-by: Sage Weil <sage@inktank.com>
ceph_test_rados: identify write seq_num in output

Signed-off-by: Sage Weil <sage@inktank.com>