Avoid trying to set db_host with an empty value

NEWS.rst

@@ -2,6 +2,11 @@
 History
 =======
 
+16.5.1
+------
+
+Avoid trying to set db_host with an empty value.
+
 16.5.0
 ------
 

odoo_scripts/docker_dev_start.py

@@ -766,8 +766,8 @@
                 _logger.info("You can add the --create-user argument to create it")
                 return 16
 
-    arg.append("--db_host")
-    arg.append(db_host)
+        arg.append("--db_host")
+        arg.append(db_host)
 
     # --- restore ---
     # TODO find out why odoo_help would stop us from restoring