Run serial_tests after all other discovered tests

In order to avoid blocking plugin tests execution
serial tests should be run after plugin tests
in each worker.

Change-Id: Ie9f984a86fbb433008e09bd2a818de5860798f35
Related-Prod: https://mirantis.jira.com/browse/PRODX-38846
(cherry picked from commit d676dff19788babfa94299d3e58aab89925e462c)
1 file changed