ReplicatedPG: copy: switch CopyCallback to use a GenContext

Signed-off-by: Greg Farnum <greg@inktank.com>
ReplicatedPG: assert that we have succeeded in do_osd_ops on copyfrom repeats

Our callback is handling errors on its own at this point.

Signed-off-by: Greg Farnum <greg@inktank.com>
ReplicatedPG: copy: don't leak a ctx on failed copy ops

Signed-off-by: Greg Farnum <greg@inktank.com>
ReplicatedPG: copy: add op progression output

Signed-off-by: Greg Farnum <greg@inktank.com>