Improve README

Add examples on how to use tasks to manage virtual machines, install
satellite and nightly builds and how to specify a ssh key when running
fabric.
Merge pull request #34 from elyezer/improve-readme

Improve README
Add vm_list_base task

The vm_list_base task will list all available base images. Update README
to show how to use the vm_list_base task.

Also improve the vm_list to only show running virtual machines by
default.
Merge pull request #35 from elyezer/vm-list

Add vm_list_base task
Fix repository headline in README

Related to #37
Clean up README.md

* Fix a broken link to robottelo.
* Add instructions for installing prerequisites.
* Wrap all text at 80 characters.
Merge pull request #36 from Ichimonji10/readme

Clean up README.md
Enable Python 3 compatibility

Make the StringIO import conditional. Add parentheses to print statements.
Refactor function "subscribe"

Try to make the function easy to read, and do make the function
pylint-compliant.
Merge pull request #38 from Ichimonji10/refactor-and-compat

Enable Py 3 compat, refactor function
Add iso_download task

The task accept both file and directory URLs for download an ISO image.
By specifying a directory the task will look for SUM files to fetch the
ISO filename, this is useful to grab the latest ISO image.
Merge pull request #39 from elyezer/iso-download-task

Add iso_download task