Test test_forbid_offline_migrations_starting_newton from
neutron.tests.functional.db.test_migrations.TestModelsMigrationsMysql
module can also fail because of db timeouts when are running on
overloaded test node.
To not fail job because of that, this patch adds skip_if_timeout
decorator to this additional test.
Change-Id: Ia255d331cbb24e1fdd12212580e85423da242eae
Related-Bug: #1687027