Fix pip not installing dependencies for bfg

[Sirozha1337]

In the docs for Bfg, it says:

pip: Install python modules with pip install --user before the test. If you need multiple modules use multiline options

So, the yaml config like this should work:

bfg:
  pip: >
      dep1

      dep2

But when you specify dependencies in .yaml file, pip is throwing this exception:

AttributeError: 'thread._local' object has no attribute 'indentation'

Upgrading pip doesn't help as pip.main is not available in the recent versions. In the pip docs, they encourage you to use subprocess, so I've changed pip.main to subprocess.check_call and now it works.

[fomars]

@f2nd подтверди плиз