rgw: fix bug with (un)ordered bucket listing and marker w/ namespace

rgw: fix bug with (un)ordered bucket listing and marker w/ namespace

When listing without specifying a namespace, the returned entries
could be in one or more namespaces. The marker used to continue the
listing may therefore contain a namespace, and that needs to be
preserved. This fixes a bug in both ordered and unordered listings
where it was not preserved.

Signed-off-by: J. Eric Ivancich <ivancich@redhat.com>
(cherry picked from commit 9457abb729754458aafc07a9ee514407906a1011)

Conflicts:
	src/rgw/rgw_rados.cc
- trivial whitespace