add retry logic to peer discovery and an expiration time for peers (#1203)

* add retry logic to peer discovery and an expiration time for peers

* Restructure discovery

* Add mac build to CI

* Always return an error for Health when not linux

* Change macos workflow

* Rename macos tests

* Update DiscoverPeers messages to pass Instants. Implement PartialEq for AttServiceMessage

* update discover peer queueing to always check existing messages and extend min_ttl as necessary

* update method name and comment

* Correct merge issues

* Add subnet id check to partialeq, fix discover peer message dups

* fix discover peer message dups

* fix discover peer message dups for real this time

Co-authored-by: Age Manning <Age@AgeManning.com>
Co-authored-by: Paul Hauner <paul@paulhauner.com>

Cargo.lock

@@ -178,6 +178,12 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "assert_approx_eq"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3c07dab4369547dbe5114677b33fbbf724971019f3818172d59a97a61c774ffd"
+
 [[package]]
 name = "assert_matches"
 version = "1.3.0"
@@ -2936,6 +2942,7 @@ dependencies = [
 name = "network"
 version = "0.1.2"
 dependencies = [
+ "assert_approx_eq",
  "beacon_chain",
  "environment",
  "error-chain",