Move docker_templates to docker dir

Updated build.py to reflect this change.
Deprecate --template option and make it a noop.

Change-Id: I7cd98d1ee684a4c64984a49597159868152683b2
Partially-Implements: blueprint remove-docker-dir

README.rst

@@ -75,8 +75,7 @@ Directories
 -  etc - Contains a reference etc directory structure which requires
    configuration of a small number of configuration variables to achieve
    a working All-in-One (AIO) deployment.
--  docker\_templates - Contains jinja2 templates for the docker build
+-  docker - Contains jinja2 templates for the docker build system.
-   system.
 -  tools - Contains tools for interacting with Kolla.
 -  specs - Contains the Kolla communities key arguments about
    architectural shifts in the code base.