Use of consistent styling in magnum configure snippets

Similarly to the use of pep8 for python code, bashate style checker allows enforcing of basic guidelines, similar to pep8 and flake8 tools for Python.

bashate can enforce some rules like for example:

Whitespace Rules

* lines should not include trailing whitespace
* there should be no hard tabs in the file
* indents are 4 spaces, and all indentation should be some multiple of them
* then should be on the same line as the if
* do should be on the same line as the for

These can be individually enabled or disabled. I propose to start easy and enforce a consistent indenting (4 spaces no tabs) only for now.