add "registry" flag to "tools/build.py"

With registry flag,
build image using `tools/build.py --registry 172.22.2.81:4000`
the image name looks like `172.22.2.81:4000/kollaglue/data`
When user use kolla-ansible,
user set `docker_registry` to `172.22.2.81:4000` in `/etc/kolla/globals.yml`.

Build image using `tools/build.py -n abcd`
the image name looks like `abcd/data`
When user use kolla-ansible,
user set `docker_namespace:` to `abcd` in `/etc/kolla/globals.yml`.

build image using `tools/build.py -n abcd --registry 172.22.2.81:4000`
the image name looks like `abcd/data`
When user use kolla-ansible,
user set `docker_namespace:` to `abcd` in `/etc/kolla/globals.yml`.
user set `docker_registry` to `172.22.2.81:4000` in `/etc/kolla/globals.yml`.

With the feature, it will reduce user confusing and mistaking.

Change-Id: I18ac7a3ccec032888e35f5e9a79fc190760cc8a0
Closes-Bug: #1505056