Write userShell configuration

The code writes the the userShell if one is defined in profile.conf

documentation to go with profile.conf in install section

# default system shell is bash
# use /etc/defaults/useradd by supplying a space " "
# use the full path e.g. "/bin/zsh"
#user_shell=" "

lib/util-yaml.sh

@@ -148,6 +148,9 @@ write_users_conf(){
     echo "doReusePassword: false" >> "$conf" # only used in old 'users' module
     echo "availableShells: /bin/bash, /bin/zsh" >> "$conf" # only used in new 'users' module
     echo "avatarFilePath:  ~/.face" >> "$conf" # mostly used file-name for avatar
+    if [[ -n "$user_shell" ]]; then
+        echo "userShell:       $user_shell" >> "$conf"
+    fi     
 }
 
 write_packages_conf(){