SecretStore: do not cache ACL contract + on-chain key servers configuration (#6107)

* do not cache ACL storage contract

* when error comes before initialization

* initial KeyServerSet commit

* update_nodes_set in maintain

* do not connect to self

* fixed connection establishing

* removed println

* improved KeyServerSet tracing

* moved parsing to KeyServerSet

* re-read only when blockchain is changed

* do not try to connect if not a part of cluster

* improved logging

* fixed tests

ethcore/native_contracts/src/lib.rs

@@ -23,6 +23,7 @@ extern crate byteorder;
 extern crate ethabi;
 extern crate ethcore_util as util;
 
+mod key_server_set;
 mod registry;
 mod urlhint;
 mod service_transaction;
@@ -32,6 +33,7 @@ mod validator_report;
 
 pub mod test_contracts;
 
+pub use self::key_server_set::KeyServerSet;
 pub use self::registry::Registry;
 pub use self::urlhint::Urlhint;
 pub use self::service_transaction::ServiceTransactionChecker;