device unable to connect randomly when controller reboots

Trigger Condition

1. channel inactive.
2. recieved message can't matched yang model
3. netconf request time out.

restconf

Data tree sometimes unavailable from restconf（http）

Futures.makeChecked() wrap input exception as execution exception

if any response of edit-config carries error, commit shouldn't be sent any more

Validate对edit-config的配置做校验（包括对内容值，相互依赖逻辑关系等），
在事务的Commit前做Validate，支持Validate without activation功能
如果Validate成功，则做commit；如果失败，则做discard-changes

2018-05-21 10:55:39,201 | WARN | dispatcher-27340 | NetconfDeviceCommunicator | 224 - org.opendaylight.netconf.sal-netconf-connector - 1.5.0.Carbon | RemoteDevice{xxxxxx}: Session is disconnected, failing RPC request
2018-05-21 10:55:39,201 | TRACE | dispatcher-27340 | KeepaliveSalFacade | 224 - org.opendaylight.netconf.sal-netconf-connector - 1.5.0.Carbon | RemoteDevice{xxxxxx}: Resetting netconf keepalive timer

transaction inconsistent state need to be taken into consideration to take remedial action
this requires the transaction submission to return more precise report when failed.