FileStore::_do_clone_range: _do_copy_range encodes error in return, not errno

Signed-off-by: Samuel Just <sam.just@inktank.com>
FileStore::_do_copy_range: read(2) might return EINTR

Signed-off-by: Samuel Just <sam.just@inktank.com>
OSD: add debugging to shutdown to catch stray PGs

Signed-off-by: Samuel Just <sam.just@inktank.com>
more debugging