Add option to install require-dev dependencies when analyzing a codebase

[Nyholm]

I currently have a problem with some libraries using test files in their source. That will give me plenty of

[BC] SKIPPED: Roave\BetterReflection\Reflection\ReflectionClass "PHPUnit\Framework\TestCase" could not be found in the located source

For this specific case it is the psr/log package. (my package)

I have been hacking the output before. See how I did in Guzzle. I dont feel this is the way I should go about it though...

I would like to add these suppress messages in a config file some how.

[Ocramius]

Potentially duplicate of #77

[asgrim]

@Nyholm would #319 help this issue perhaps?

[Nyholm]

Yeah. I think that would work.

I solved it with https://github.com/Nyholm/roave-bc-check-docker#config

[asgrim]

OK; so not quite the best solution :) I'm ok to leave this issue open as a possible improvement.