Return bound port number from grpc_server_add_http2_port.

Allows tests to bind to port 0 and still have clients connect to them.
	Change on 2015/01/12 by ctiller <ctiller@google.com>
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=83800669
7 files changed