Add ability to set reactor_worker_threads

There is issue [1] with reactor in salt 2017, one
of the workarounds is to set reactor workers to 1

[1] https://github.com/saltstack/salt/issues/47539

Change-Id: I47d76cc1dc5d0afe6d8b215e2d32cdbab3ac1a8c
Related-Prod: https://mirantis.jira.com/browse/PROD-21463
2 files changed