This change adds a default value of 2 to the os_workers fact for spec
tests. This fact was added to openstacklib as part of
Ia588817fde9203a134bc9eaad9a5bd5453d7639a to be used as the default for
worker configurations within the puppet openstack management. This
change lays the groundwork to have this fact defined for unit tests as
we implement the cutover from processcount to os_workers.
Change-Id: Ic7c92385b8e6b63264f21ce7a5ab957889b8b104