Procedure is rewritten using std::partition, making it easier to
maintain and it also fixes a theoretical quadratic behavior because
list is entirely copied when extending it, which isn't harmful
because maintenance set will be rarely populated and there are only
2 sets at most.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20210409171412.57729-1-raphaelsc@scylladb.com>