Switch the csit-hwvtep-openstack to use job prefix

Switch the csit-hwvtep-openstack to use job prefix

Idea to add a new variable "{prefix}" to job templates. This
variable is defined already in defaults.yaml.
The prefix should always be blank in production thus producing the
same existing job names we are all used to. The prefix can be used
locally to add a prefix to job names when pushing jobs to the
sandbox. For example a prefix of "abc-" will be added to the front
of the job name allowing sandbox testers to be able to push a job
to the sandbox with a unique prefix to not overwrite other testers.

Additionally add an id inttest-csit-hwvtep-openstack to make the job
template more easy to maintain. Allows us to refactor the job
template name without having to update every single user of the
template every time as the id will always be the same.

Change-Id: I86685a09eb2a3b385778c4dfc7a59b45e97d1693
Signed-off-by: Thanh Ha <thanh.ha@linuxfoundation.org>