Upgrade discovery and restructure task execution (#1693)

* Initial rebase

* Remove old code

* Correct release tests

* Rebase commit

* Remove eth2-testnet dep on eth2libp2p

* Remove crates lost in rebase

* Remove unused dep

Cargo.toml

@@ -35,6 +35,7 @@ members = [
     "common/slot_clock",
     "common/test_random_derive",
     "common/warp_utils",
+    "common/task_executor",
     "common/validator_dir",
 
     "consensus/cached_tree_hash",