Wrong address (port as a part of IP) when discovering new instance

[pznamensky]

Orchestrator (v3.0.12) trying to discover IPv6 host after appending port to address.
How to reproduce:

1. Setup master-slave replication in IPv6 network
2. Use master's IPv6 address in CHANGE MASTER TO ...
3. Setup orchestrator
4. Discover topology with the following command:

~ # orchestrator -c discover -i slave1 --debug

2018-09-07 17:39:31 INFO starting orchestrator, version: 3.0.12, git commit: d318760701a5649867606f455148e28f4353d288
2018-09-07 17:39:31 INFO Read config: /etc/orchestrator.conf.json
2018-09-07 17:39:31 DEBUG Hostname unresolved yet: slave1
2018-09-07 17:39:31 DEBUG Cache hostname resolve slave1 as slave1
2018-09-07 17:39:31 DEBUG Connected to orchestrator backend: sqlite on /usr/local/orchestrator/orchestrator.sqlite3
2018-09-07 17:39:31 DEBUG Initializing orchestrator
2018-09-07 17:39:31 INFO Connecting to backend :3306: maxConnections: 128, maxIdleConns: 32
2018-09-07 17:39:31 DEBUG Hostname unresolved yet: 2abc::1
2018-09-07 17:39:31 DEBUG Cache hostname resolve 2abc::1 as 2abc::1
2018-09-07 17:39:31 DEBUG Hostname unresolved yet: 2abc::1
2018-09-07 17:39:31 DEBUG Cache hostname resolve 2abc::1 as 2abc::1

5. Error occurs:

2018-09-07 17:39:39 ERROR dial tcp [2abc::1:3306]:3306: i/o timeout
2018-09-07 17:39:39 ERROR ReadTopologyInstance(2abc::1:3306): dial tcp [2abc::1:3306]:3306: i/o timeout
WARNING: NamedStopwatch.Stop("instance") IsRunning is false
2018-09-07 17:39:39 WARNING  DiscoverInstance(2abc::1:3306) instance is nil in 2.003s (Backend: 0.002s, Instance: 2.001s), error=dial tcp [2abc::1:3306]:3306: i/o timeout

As you can see orchestrator trying to connect to [2abc::1:3306]:3306 instead of [2abc::1]:3306

[shlomi-noach]

Similar: github/gh-ost#604

[shlomi-noach]

This is going to be a problem. Very initial work (to refactor some underlying mechanisms) is in #623 , but the way is long till ipv6 is supported. I'm afraid there's much assumption about hostname:port being the way to represent a listening server, and it will impact much of the code to fix that.