move docker-build groovy script to docker repo

move docker-build groovy script to docker repo

For all docker builds, policy is using groovy-maven-plugin
to run a groovy script to determine the tag for docker.

The plan is:
1, move docker-tag groovy script to docker repo.
2, change source for groovy-maven-plugin to a URL
   below, that will point to the source code from
   step #1.

   <configuration>
       <source>https://raw.githubusercontent.com/onap
       /policy-docker/master/utils/groovy
       /docker-tag.groovy</source>
   </configuration>

Issue-ID: POLICY-3378
Change-Id: Iff1f09e5ae47205240305b09602c49d403fad98f
Signed-off-by: Taka Cho <takamune.cho@att.com>