Allow to specify the group id in the groups list a user
should belong to. The group id can be placed as part of
the group name separated by a colon like in the following
example:
<users>
<user groups="kiwi,admin:42,users" password="..." name="kiwi"/>
</users>
Please note kiwi checks if the provided group already
exists and only creates a group if it is not already present in
the system. As default groups are usually provided by the OS
itself including its preferred group id, you will intentionally
not be able to overwrite group id for existing groups.
This Fixes#2064
04d966b920