[cdc_stream] Use ephemeral ports (#100)

Instead of running netstat/ss on local and remote systems, just bind
with port 0 to find an ephemeral port. This is much more robust,
simpler and a bit faster. Since the remote port is only known after
running cdc_fuse_fs, port forwarding has to be set up after running
cdc_fuse_fs.

cdc_stream/BUILD

@@ -214,6 +214,7 @@ cc_library(
         "//common:process",
         "//common:remote_util",
         "//common:sdk_util",
+        "//common:server_socket",
         "//common:status_macros",
         "//common:stopwatch",
         "//data_store:disk_data_store",