create container user with no user group

This issue was reported in #123, where @miellaby wrote:

> Context: Using cqfd from a host user (jenkins) who has no user
> group. For example, on our server, jenkins belongs to the docker group
> only (which is its primary group).
>
> Expected: commands run by cqfd inherits the credentials/ownership of
> the host user. Especially files generated by cqfd encapsulated
> commands have the same user and group than the files generated without
> cqfd. In our case, generated files should be owned by
> jenkins:docker (user jenkings group docker).
>
> Observed: files generated within cqfd are owned by jenkins:jenkins
> instead of jenkins:docker.
>
> Correction proposal (TBC): In make_launch() bash function, useradd
> should be called with the --no-user-group (-N) option to make the
> docker user consistent with the host user (that is with the same
> primary group).

cqfd

@@ -367,7 +367,7 @@ test_su_session_command && has_su_session_command=1
 
 # Add the host's user and group to the container, and adjust ownership.
 groupadd -og $GROUPS -f builders || die "groupadd command failed."
-useradd -s /bin/sh -ou $UID -g $GROUPS -d "$cqfd_user_home" $cqfd_user \
+useradd -s /bin/sh -oN -u $UID -g $GROUPS -d "$cqfd_user_home" $cqfd_user \
 	|| die "useradd command failed."
 mkdir -p "$cqfd_user_home" || die "mkdir command failed."
 chown $UID:$GROUPS "$cqfd_user_home" || die "chown command failed."