pip install path remap

[j0yu]

Closes #861
Closes #863

New configuration setting to allow people to map and configure rez-pip --install of unknown RECORD paths.

For example, for #861, a new entry like so can be added to capture and re-map and move all ../../* paths that are unknown/not handled by rez-pip to just live under the root rez package installation like so:

# Inside rezconfig.py...
pip_install_remaps = [

    # ...add these before the end

    # # Fix for greenlet in https://github.com/nerdvegas/rez/issues/861
    # Path in record          | pip installed to    | copy to rez destination
    # ------------------------|---------------------|--------------------------
    # usr/local/*             | *                   | python/*
    {
        "record_path": r"(.*){sep}usr{sep}local{sep}(.*)",
        "pip_install": r"\1{sep}usr{sep}local{sep}\2",
        "rez_install": r"\2",
    },

    # # Fix for Qt.py in https://github.com/nerdvegas/rez/issues/861
    # Path in record          | pip installed to    | copy to rez destination
    # ------------------------|---------------------|--------------------------
    # ../../NOT PARDIR        | *                   | *
    {
        "record_path": r"^{p}{s}{p}{s}(?!{p})(.*)",
        "pip_install": r"\1",
        "rez_install": r"\1",
    },
]

@smaragden, want to give these a test?

---

Added

• rez.config.PipInstallRemaps setting to extend validate to perform token substitutions for...
• ...new rez.rezconfig.pip_install_remaps setting

Changed

• More detailed error message for unknown source file
• Tidied imports in rez.pip

[zachlewis]

Thanks @j0yu, I think this is pretty effective. The error message with the detailed instructions is really helpful, and the tokens are quite nice. This helped me rez-pip install ipykernel, which was having similar trouble with stuff in '../../share/*'

[nerdvegas]

Real clean @j0yu cheers,
A