Build fails when changing git branch during the build

[Martin André]

When we're not providing a tag, the build script will use one based on the short SHA of the tip of the current git branch.

The `build-all-docker-images` script should always provide a tag to `build-docker-image` in order to prevent issues with Docker not being able to find the base image when changing branches during an ongoing build.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/183508
Committed: https://git.openstack.org/cgit/stackforge/kolla/commit/?id=2844a2510249a200f87d8d173ce5da9f1361757c
Submitter: Jenkins
Branch: master

commit 2844a2510249a200f87d8d173ce5da9f1361757c
Author: Martin André <email address hidden>
Date: Tue May 26 10:59:49 2015 +0900

    Always provide a tag when building with build-all-docker-images

    When we're not providing a tag, the build script will use one based on
    the short SHA of the tip of the current git branch.

    Make the `build-all-docker-images` script always provide a tag to
    `build-docker-image` in order to prevent issues with Docker not being
    able to find the base image when changing branches during an ongoing
    build.

    Closes-Bug: #1458739
    Change-Id: Id6925b792f46d14b20a7dbebfaf0d351ddec6538