create a function to determine indentation

[bastelfreak]

based on this:
#200 (comment)

in our Gemfile template, we do really balck magic to determine the indentation. We should create a seperate function to make it more readable.

[igalic]

relatedly, from discussion on irc:

i wonder if we can put this try monad from voxpupuli/network in some reusable shape into voxpupuli/extlib