Updated Dockerfile, added Jenkinsfile.

[chadduffin]

An updated Dockerfile is important so that anyone can build and run W3AF anywhere. Along with being able to build it, it is useful to be able to build this image with CI so that the most up to date version can be easily and automatically maintained.

This pull request contains:

• An updated Dockerfile.
  • More recent base image is being used.
  • Layers have been significantly compacted.
  • Pip dependencies have been fixed and update.
  • Updated deprecated directives.
• A Jenkinsfile.
  • This pipeline performs the build, push and cleaning steps that typically occurred in the provided build script.
  • Functional, was used to push this image: https://hub.docker.com/r/liatrio/w3af/
• 'simple-docker-build.sh'
  • Provides basic Docker build functionality.
• Miscellaneous file with references to Pip dependencies updated to match Dockerfile.
• Previous Dockerfile backed up in /extras/docker/ubuntu:12.04.

[andresriancho]

Thanks for this great PR, the dockerfile needed some maintenance 👍

Some of my comments went inline with the code, some other comments here:

• Jenkinsfile: w3af uses circleci for builds (see circle.yml in root directory). When a build succeeds then a new docker image is build and pushed. Builds haven't been passing for some time now... that it why we don't get fresh docker images in hub.docker.com. Please remove this file since we won't use it: adding another build system doesn't make much sense.

• Please send the PR against the develop branch which has significant improvements from master and, for example, a different set of pip requirements.

[andresriancho]

I believe that we can safely remove this file, we don't really need the backup.

[andresriancho]

Just upgraded develop to use this lib version

[andresriancho]

The develop branch already uses a newer version