Move Dockerfile to ./docker path

Move Dockerfile to ./docker path

According to other projects(releng/jjb/releng/opnfv-docker.yml), all the
Dockerfiles are put in ./docker path.

The escalator docker build procedure will be seperated from escalator tar file
build procedure. The escalator docker will be directly used during the tar
build procedure. It will help to save the build time.

A seperate job will be created in Jenkins to monitor the Docker changes
and will build the docker image.

Change-Id: I815a8b1043bb0e3b614fa56d0fb793c1c9eb1a0e
Signed-off-by: zeyu zhu <zhu.zeyu@zte.com.cn>