resolve offence in latest rubocop

apparently it now checks Gemfile, too.
add comment reminder about minimum golang version for bugfix

resolves https://github.com/jumanjiman/wormhole/issues/35
add xmlstarlet to manipulate xml files from shell

> XMLStarlet is a set of command line utilities which can be used
> to transform, query, validate, and edit XML documents and files
> using simple set of shell commands in similar way it is done for
> plain text files using UNIX grep, sed, awk, diff, patch, join, etc
> commands.

resolves https://github.com/jumanjiman/wormhole/issues/31
do not attempt to install golang-docs

resolves yum message:

> No package golang-docs available.
upgrade to docker v1.1.2 on wercker box
devenv: add pykickstart to development env

I am adding pykickstart so that we have ksvalidate available in the
dev env when working with our kickstart files and scripts.