This string comes from an authority field, which is allowed to contain a
':' port (see https://tools.ietf.org/html/rfc3986#section-3.2).

We need to strip it before performing host name verification.

This makes grpc.early_adopter much more independent of RPC
Framework and cleaner at the cost of reexporting most of the
interfaces and writing several delegation classes.

After we have called closed() ensure that no other callbacks are ever made.

- Added a way to override the cipher suites with an environment
  variable so that we can still do interop testing with java7.
- Takes care of #681.

- Should fix #746.

Instead, we do a shutdown() at the point we are currently closing, to
kick off socket teardown while ensuring an fd ref is sufficient to make
concurrent syscalls like epoll_ctl safe.