Fixed problems handling passive connections in Remoting #2878

- Fixed potential race in EndpointWrite when TakeOff is processed
- Reenabled accidentally disabled gremlin due to changed defaults
- Fixed EndpointRegistry incorrectly handling passive connections
Shut down both client and server channels. See #2862
Clean up network connections from the test coordinator and player. See #2862
Merge pull request #1037 from akka/wip-2862-leaking-netty-threads-ban

Leaking Netty threads causes file handle exhaustion
Merge pull request #1031 from drewhk/wip-2780-removal-of-old-remoting-drewhk

Removed remaining parts of the old remoting #2780