fix add_user script

confd/templates/add_ldap_user.tmpl

@@ -5,6 +5,7 @@ usage() {
 usage: docker exec [...] add_ldap_user [-c COMMON_NAME] [-s SURNAME] [-u UID] [-p PASSWORD] [-e EMAIL]
   Unset options will be prompted interactively.
 EOF
+}
 
 COMMON_NAME=
 USER_UID=
@@ -74,7 +75,7 @@ assert "User already present. Please choose a different UID."
     echo -n "Enter user email (leave blank for ${USER_UID}@${LDAP_DOMAIN}) > "
     read USER_EMAIL
 }
-[[ -n ${USER_EMAIL} ]] || USER_EMAIL="${USER_UID}@${LDAP_DOMAIN}"
+USER_EMAIL="${USER_EMAIL:=${USER_UID}@${LDAP_DOMAIN}}"
 
 
 PWHASH=$(slappasswd -h "{SSHA}" -s "${USER_PASS}")