Get rid of prima donna methods

Remove the methods which use the exclamation mark suffix without
another method without the suffix being available.

Also use consistent naming for the validation functions.

See also: https://github.com/troessner/reek/wiki/Prima-Donna-Method
Remove obsolete class variable
Removed RPM dependencies to kiwi and python-glanceclient
Merge pull request #253 from SUSE/review_140930_saner_dependencies_for_machinery_package

Removed RPM dependencies to kiwi and python-glanceclient
Merge branch 'remove_obsolete_variable'

Pull request #251
Add rubygem-devel as explicit requirement for 13.1

It seems that the handling of Ruby gems for openSUSE 13.1 was changed. A
backport repository is automatically used and ruby-devel needs to be
required explicitly.
Merge pull request #260 from SUSE/add_ruby-devel_as_13.1_requirement

Add rubygem-devel as explicit requirement for 13.1
Merge branch 'remove_primadonnas'

Pull request #250
Implement HTML view on system descriptions

This commit adds two new commands to Machinery for creating and showing
an HTML view of system descriptions:

1. machinery generate-html DESCRIPTION

Generates the according HTML page (index.html) and puts it in the system
description directory.

2. machinery show DESCRIPTION --html

generates the HTML page and opens it in the browser using "xdg-open".

With this commit we also dynamically generate scope documentation for
the man page and the HTML exports from one source (markdown files in
plugins/docs/)