fix(db-create): don't force to use --drop if there is no existing db.

related: #202

cubicweb/server/serverctl.py

@@ -403,12 +403,17 @@ class CreateInstanceDBCommand(Command):
                             ASK.confirm('Create db user %s ?' % user, default_is_yes=False)):
                         helper.create_user(source['db-user'], source.get('db-password'))
                         print('-> user %s created.' % user)
-                if dbname in helper.list_databases(cursor) and should_drop_db():
-                    cursor.execute('DROP DATABASE "%s"' % dbname)
-                else:
-                    print('you may want to run "cubicweb-ctl db-create '
-                          '--drop %s" to continue.' % config.appid)
-                    return
+                if dbname in helper.list_databases(cursor):
+                    if should_drop_db():
+                        cursor.execute('DROP DATABASE "%s"' % dbname)
+                    else:
+                        print(
+                            'The database %s already exists, but automatically dropping it '
+                            'is currently forbidden. You may want to run '
+                            '"cubicweb-ctl db-create --drop=y %s" to continue or '
+                            '"cubicweb-ctl db-create --help" to get help.'
+                            % (dbname, config.appid))
+                        raise Exception('Not allowed to drop existing database.')
                 createdb(helper, source, dbcnx, cursor)
                 dbcnx.commit()
                 print('-> database %s created.' % dbname)