fix #686 encode credentials in install case

[oleastre]

Quick fix for #686
This PR just fixes the install code path as the other one seems to forward the credentials to other components that should properly generate their own url.

[kasteph]

@oleastre Thanks for your PR!

This is a duplicate of #1341 (which has a test) so I will close this PR.

[oleastre]

#1341 fixes the develop branch while this one fixes the master branch.
The code that generates the index url is contained in the installer object and not in the repository like in the new develop version.
And there is no existing test for the pip_installer.install method on master. So I did not created one from scratch.
But if absolutely required to solve that bug, I can write one.

[chrispblink]

Just in case someone ends up here trying to make poetry 0.12.* work with 19.* and private repos and special chars in your creds: check out this little wrapper utility called pooetry

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.