Use RFC 3986 compliant addresses in log messages

When log messages are written with both address and port information, IPv6
addresses can cause confusion if the normal address:port formatting is
used. The RFC 3986 suggests that all IPv6 addresses are expressed as a
bracket enclosed address optionally followed by the port that is separate
from the address by a colon.

In practice, the "all interfaces" address and port number 3306 can be
written in IPv4 numbers-and-dots notation as 0.0.0.0:3306 and in IPv6
notation as [::]:3306. Using the latter format in log messages keeps the
output consistent with all types of addresses.

The details of the standard can be found at the following addresses:

     https://www.ietf.org/rfc/rfc3986.txt

     https://www.rfc-editor.org/std/std66.txt

Documentation/Release-Notes/MaxScale-2.1.2-Release-Notes.md

@@ -15,6 +15,25 @@ report at [Jira](https://jira.mariadb.org).
 
 ## Changed Features
 
+### Formatting of IP Addresses and Ports
+
+All messaging that contains both the address and the port are now printed in an
+IPv6 compatible format. The output uses the format defined in
+[RFC 3986] (https://www.ietf.org/rfc/rfc3986.txt) and
+[STD 66] (https://www.rfc-editor.org/std/std66.txt).
+
+In practice this means that the address is enclosed by brackets. The port is
+separated from the address by a colon. Here is an example of the new format:
+
+```
+[192.168.0.201]:3306
+[fe80::fa16:54ff:fe8f:7e56]:3306
+[localhost]:3306
+```
+
+The first is an IPv4 address, the second an IPv6 address and the last one is a
+hostname. All of the addresses use port 3306.
+
 ### Cache
 
 * The storage `storage_inmemory` is now the default, so the parameter