Mini: fix tablet hostname

[artemvovk]

So that this container can work with a non-host network

Signed-off-by: avovk@recurly.com

I have a docker network and MySQL running in a container on that network.
Using the following docker run:

docker run -it --hostname vitess --name vitess -e "TOPOLOGY_SERVER=db:3306" -e "TOPOLOGY_USER=root" -e "TOPOLOGY_PASSWORD=dev" -e "MYSQL_SCHEMA=development" --network="development" vitess/mini:latest

I kept running into timeouts from vtctlclient.

vitess@23cc1adb9441:/$ vtctlclient TabletExternallyReparented zone1-0000000100
E0729 23:04:55.257453     914 main.go:67] remote error: rpc error: code = Unavailable desc = transport is closing

Finally, identified that hostname:port for that command were not the ones where vttablet was listening.

I retested this using --network=<custom> and --network=host.

[dkhenry]

Looks like it will work under all circumstances.