Respect nodename in `server_info_test` (#2959)
Respect nodename in `server_info_test` (#2959)

Summary:
On some machines, including standard Ubuntu 16.04, binding to `::1` and
then trying to open an HTTP connection to `localhost` can in some cases
try to connect only over IPv4, which fails. This commit changes a test
to connect to the node name given by the socket rather than hard-coding
`localhost`.

Test Plan:
Tested in an upcoming GitHub Actions workflow. Googlers, see test sync:
<http://cl/281679857>

wchargin-branch: serverinfotest-nodename
tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard