Renovate: Support setup.py with nested references

[rarkins]

setup.py Renovation is now in beta.

This setup.py contains references to requirements/*.pip files in the same repo.

When using non-gitFs, this results in a hard fail of parsing setup.py. Using gitFs=https, it's a soft fail: no dependencies detected.

If I instead configure like so:

  "pip_requirements": {
    "fileMatch": ["requirements/*"]
},

Then these .pip files are detected as pip_requirements files and an upgrade is found.

Questions for @hutson:

1. Do you think it's common for setup.py to include external requirements like this?
2. Was this only done so that you could treat them as requirements.txt files?
3. Do you think it's likely anyone would externalise setup.py files and not have them in pip requirements format?
4. Do you think Renovate should look for *.pip files by default?

[hutson]

I believe the configuration suggestion is good enough for our use case.

1. I have not seen this approach before, but I have heard it's used elsewhere.
2. The approach was taken to keep setup and maintenance of the files simple.
3. I don't know.
4. In our case, no. The suggested configuration should be fine for our use case.

[rarkins]

For now, we will support just versions contained within the setup.py. If someone has a real use case you think deserves support and you find this issue, please explain more about it below.