Regularize server factories #29
Description
The server factory has a different notion of what an "address" is to the client factory. This is awkward.
I don't like the way the DefaultGrpcServerFactory takes an address (which is actually a host) and a port in the constructor. It also seems like we should aim to use Grpc.newServerBuilderForPort(port, creds) instead of the netty-specific versions. The netty-specific parts of the factory could then be isolated to creating the ServerCredentials, in principle. In practice I don't know if that would easily allow the "unix:" pseudo-scheme that we currently support.
If we get this right it should make it easier to add other server implementations (there's an okhttp one).