Refactor templates and scripts for container tag

Refactor templates and scripts for container tag

Change parameter names used to specify container tag method,
with a new default to use the fixed string 'latest' as a tag.
Merge two shell scripts into one instead of using Jenkins
conditional steps.
Extend to accept a custom directory for the container-tag.yaml
if the yaml-file method is used to set the docker tag information;
this is an optional variable which is set to empty by default,
and falls back to DOCKER_ROOT.

Signed-off-by: Lott, Christopher (cl778h) <cl778h@att.com>
Change-Id: I19a8809650fa29706acaf0f06f4b666bef0067d7