Change fe83b5488d33b75be6a9bba97faa8ddd69210973 enforced usage of IPv6
in case the scenario requires IPv6, but this causes the following
failure during rabbitmq startup, because hostname is sometimes resolved
to IPv4 address in CI.
```
ERROR: epmd error for host np0033504771: badarg (unknown POSIX error)
```
This makes sure that hostname env is set according to IP address
version.
Change-Id: I4d876200f0fd8b2b84d893f243fe5615352ef11d