Add support for using different docker images

The part of trying out scripts involve creating a docker container with
ssh and running some projects and functions on it.

This change allows to define the docker image name to be used with the
docker-* functions.
Add yum support to kickstart.package functions

Yum only supports passing one package to check its info.
Other package managers allow you to have several packages name, and
return non-zero whenever one is not installed.

To have the same behaviour on yum, we iterate over the list until we
find one that is not installed.
Add kickstart to PATH under ~/.bash_profile to work with systems that does not use ~/.bashrc by default
Use release files to identify distro

Docker can run a different distro from the host. For example, Ubuntu
host with CentOS docker image.

The container uses the same kernel as the host tho. On a CentOS
container under Ubuntu, `uname -a` will report it to be an Ubuntu
kernel.

Linux distros comes with configuration files under `/etc` that helps
identify the family it is. An example of configuration files to help
identify is on http://linuxmafia.com/faq/Admin/release-files.html