Release 1.7.0

[patapenka-alexey]

This release adds to the graphite plugin ability to send metrics
to the multiple servers and hide replication metrics of the deleted
replica.

Added

• graphite: ability to send metrics to the multiple servers.
  Backward compatibility with previous plugin version is preserved.
  From now on init method assigns an unique name to the created fiber
  using incoming graphite server opts (if passed). Added new stop()
  method to stop all fibers started by the plugin (graphite: multiple servers support #540).

Fixed

• Deleting a replica via box.space._cluster:delete() doesn't delete
  information about this replica from the metrics (it's gone only
  after cluster is restarted) (replication: remove metrics of the removed replicas #538).