advertise client urls accepts empty hosts

[heyitsanthony]

A command line misconfiguration from irc:

$ SPELLEDOK="localhost"
$ etcd --listen-client-urls=http://127.0.0.1:2379 --advertise-client-urls=http://$SPELEDOK:2379 &
$ etcdctl member list
8e9e05c52164694d: name=default peerURLs=http://localhost:2380 clientURLs=http://:2379 isLeader=true

etcd should probably detect empty advertise hostnames and exit with an error.

/cc @kbrwn

[xiang90]

/cc @harryge00 would you like to help on this one?

[shubheksha]

Hi, I'd like to work on this issue if it's not taken already. This would be my first contribution so I'd appreciate some help regarding where to get started. 😄

[gyuho]

@shubheksha That would be great. Please start from #8384 as reference. And let us know if you need more help.

Thanks!

[xiang90]

fixed by #8786