Prior to this commit parsing addresses had an inconsistent effect on the
various properties that can be contained in an address (host, port,
username, password, and virtual host).

Three different approaches were used:

1. Return the property if no addresses were set. If there was one
   address set, return the property from the address. Otherwise return
   null. (host)
2. Return the property if no address were set, otherwise return the
   property from the first address (port)
3. Return the property if no addresses were set, otherwise return the
   property from the last address that had such property (username,
   password, virtual host).

This commit aims to make the behaviour consistent. If no addresses
were set the property is returned. Otherwise the value extracted from
the first address is returned. If the first address has no such value
the property is returned.

Closes gh-6424