Make error message (for missing verified email) work with Test PyPI

[brainwane]

Right now, when someone tries to upload a package to PyPI but does not have a verified email address on file, the error message we send them includes -- hardcoded -- the URL https://pypi.org. Instead, we should use Pyramid's URL routing to refer to the URL of the PyPI in question, thus ensuring that we send error messages that, as appropriate, refer to pypi.org, test.pypi.org, or any other future PyPI.

To fix this, look at warehouse/forklift/legacy.py and tests/unit/forklift/test_legacy.py (the test is test_upload_requires_verified_email), and make changes similar to the changes I made in #3183. If you're used to string substitution/string formatting in Python, this should be a pretty approachable first Warehouse issue.

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[nitinprakash96]

I'm willing to work on this one. I'll let you know about the further progress @brainwane

[brainwane]

Sounds good. @nitinprakash96 you go ahead and work on this one, and @saxenanurag can concentrate on #3185 instead. :)