[FIX] module_auto_update: Rollback cursor if param exists

Without this patch, when upgrading after you have stored the deprecated features parameter, the cursor became broken and no more migrations could happen. You got this error:

    Traceback (most recent call last):
    File "/usr/local/bin/odoo", line 6, in <module>
        exec(compile(open(__file__).read(), __file__, 'exec'))
    File "/opt/odoo/custom/src/odoo/odoo.py", line 160, in <module>
        main()
    File "/opt/odoo/custom/src/odoo/odoo.py", line 157, in main
        openerp.cli.main()
    File "/opt/odoo/custom/src/odoo/openerp/cli/command.py", line 64, in main
        o.run(args)
    File "/opt/odoo/custom/src/odoo/openerp/cli/shell.py", line 65, in run
        self.shell(openerp.tools.config['db_name'])
    File "/opt/odoo/custom/src/odoo/openerp/cli/shell.py", line 52, in shell
        registry = openerp.modules.registry.RegistryManager.get(dbname)
    File "/opt/odoo/custom/src/odoo/openerp/modules/registry.py", line 355, in get
        update_module)
    File "/opt/odoo/custom/src/odoo/openerp/modules/registry.py", line 386, in new
        openerp.modules.load_modules(registry._db, force_demo, status, update_module)
    File "/opt/odoo/custom/src/odoo/openerp/modules/loading.py", line 335, in load_modules
        force, status, report, loaded_modules, update_module)
    File "/opt/odoo/custom/src/odoo/openerp/modules/loading.py", line 239, in load_marked_modules
        loaded, processed = load_module_graph(cr, graph, progressdict, report=report, skip_modules=loaded_modules, perform_checks=perform_checks)
    File "/opt/odoo/custom/src/odoo/openerp/modules/loading.py", line 136, in load_module_graph
        registry.setup_models(cr, partial=True)
    File "/opt/odoo/custom/src/odoo/openerp/modules/registry.py", line 186, in setup_models
        cr.execute('select model, transient from ir_model where state=%s', ('manual',))
    File "/opt/odoo/custom/src/odoo/openerp/sql_db.py", line 154, in wrapper
        return f(self, *args, **kwargs)
    File "/opt/odoo/custom/src/odoo/openerp/sql_db.py", line 233, in execute
        res = self._obj.execute(query, params)
    psycopg2.InternalError: current transaction is aborted, commands ignored until end of transaction block

Now you can safely migrate, be that parameter pre-created or not.

module_auto_update/migrations/9.0.2.0.0/pre-migrate.py

@@ -12,10 +12,12 @@ _logger = logging.getLogger(__name__)
 def migrate(cr, version):
     """Autoenable deprecated behavior."""
     try:
-        cr.execute(
-            "INSERT INTO ir_config_parameter (key, value) VALUES (%s, '1')",
-            (PARAM_DEPRECATED,)
-        )
+        with cr.savepoint():
+            cr.execute(
+                """INSERT INTO ir_config_parameter (key, value)
+                   VALUES (%s, '1')""",
+                (PARAM_DEPRECATED,)
+            )
         _logger.warn("Deprecated features have been autoenabled, see "
                      "addon's README to know how to upgrade to the new "
                      "supported autoupdate mechanism.")