credentials/alts: Support UDS addresses in ALTS interop test server (#2763)
credentials/alts: Support UDS addresses in ALTS interop test server (#2763)

* Support UDS addresses in ALTS interop test server

* Fix flag description

* Fixed comment

* Fix comment

stanley-cheung/grpc-go,dfawley/grpc-go,menghanl/grpc-go,dfawley/grpc-go,menghanl/grpc-go,grpc/grpc-go,grpc/grpc-go,stanley-cheung/grpc-go