Add a abstract_replication_strategy::get_primary_ranges() method, which is
very similar to the existing get_ranges(), except that only the "primary"
owner of each range will return it in its list.
This is needed for the "primary range" repair option, which asks to repair
only the primary range. This option is useful when the user plans to start
a repair on *all* nodes, we shouldn't repair the same token range multiple
times, so each range should be repaired by only one of the nodes.
abstract_replication_strategy::get_primary_ranges() is similar to Origin's
StorageService.getPrimaryRangesForEndpoint().
Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>
e7ef6149d7