crimson: s/crimson::do_until/crimson::repeat/

crimson: s/crimson::do_until/crimson::repeat/

seastar::do_until() takes a predicate functor and a continuation. while
seastar::repeat() takes a single continuation which returns
stop_iteration::yes or stop_iteration::no. in general, we want to mirror
and extend the facilities offered by seastar instead of changing it in
an unexpected way. while crimson::do_until() only take a single
continuation which returns a bool. in hope to be more consistent, in
this change, all occurances of crimson::do_until are replaced with
crimson::repeat.

Signed-off-by: Kefu Chai <kchai@redhat.com>