common/bl, *: deprecate list::claim() in favor of operator=(list&&).

common/bl, *: deprecate list::claim() in favor of operator=(list&&).

The motivation is that `claim(list&)` seems to actually be a pre-C++11
counterpart of the already available `operator=(list&&)`.
This commit deprecates the `claim()` method but doesn't drop it yet.

All occurrences of `buffer::list::claim(list&)` are switched to
  * `list::operator=(list&&)` or
  * reworked to use `list::list(list&&)` instead.

Changes are applied to: rgw, osdc, osd, os/memstore, os/filestore,
os/bluestore, os, msg, mgr, messages, mds, librbd, librados, crimson,
common, cls, mon.

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>