update deputy middleware to properly close channel between connections

[nicktur100]

Change deputy middleware to open a new channel, rather than use a sub-channel and edit the Peers list.
From tchannel code:

// Remove removes a peer from the peer list. It returns an error if the peer cannot be found.
// Remove does not affect connections to the peer in any way.

Observed that with the subchannel implementation, connections using deputy would work sporadically, especially soon after a service restart, but would start failing later, possibly after the Cerberus CLI session was restarted.

Creating a new channel and closing it is consistent with the more generic middleware supported by Cerberus/Deputy team.

See https://code.uberinternal.com/T4892307 for internal Uber details

[claassistantio]

All committers have signed the CLA.

[coveralls]

Coverage decreased (-0.04%) to 69.803% when pulling 28e2ad0 on nturner/deputy-fix into e668e50 on master.