Resumable warp-sync / Seed downloaded snapshots (#8544)

* Start dividing sync chain : first supplier method

* WIP - updated chain sync supplier

* Finish refactoring the Chain Sync Supplier

* Create Chain Sync Requester

* Add Propagator for Chain Sync

* Add the Chain Sync Handler

* Move tests from mod -> handler

* Move tests to propagator

* Refactor SyncRequester arguments

* Refactoring peer fork header handler

* Fix wrong highest block number in snapshot sync

* Small refactor...

* Resume warp-sync downloaded chunks

* Add comments

* Refactoring the previous chunks import

* Fix tests

* Address PR grumbles

* Fix not seeding current snapshot

* Address PR Grumbles

* Address PR grumble

* Retry failed CI job

* Update SnapshotService readiness check
Fix restoration locking issue for previous chunks restoration

* Fix tests

* Fix tests

* Fix test

* Early abort importing previous chunks

* PR Grumbles

* Update Gitlab CI config

* SyncState back to Waiting when Manifest peers disconnect

* Move fix

* Better fix

* Revert GitLab CI changes

* Fix Warning

* Refactor resuming snapshots

* Fix string construction

* Revert "Refactor resuming snapshots"

This reverts commit 75fd4b553a38e4a49dc5d6a878c70e830ff382eb.

* Update informant log

* Fix string construction

* Refactor resuming snapshots

* Fix informant

* PR Grumbles

* Update informant message : show chunks done

* PR Grumbles

* Fix

* Fix Warning

* PR Grumbles

ethcore/sync/src/tests/snapshot.rs

@@ -80,6 +80,10 @@ impl SnapshotService for TestSnapshotService {
 		Some((1, 2))
 	}
 
+	fn completed_chunks(&self) -> Option<Vec<H256>> {
+		Some(vec![])
+	}
+
 	fn chunk(&self, hash: H256) -> Option<Bytes> {
 		self.chunks.get(&hash).cloned()
 	}