WIP: Raise exception from subprocess.check_output before actually calling …

[AdamGold]

Thank you for contributing to Pipenv!

WIP

The issue

1. Errors if WORKON_HOME is not writable could be better #2553
2. errors from subprocess not being caught
3. misc.py called sys.stderr with 3 arguments instead of 1.

The fix

call subprocess.check_output before Popen and raise exceptions.

The checklist

• Associated issue
• A news fragment in the news/ directory to describe this fix with the extension .bugfix, .feature, .behavior, .doc. .vendor. or .trivial (this will appear in the release changelog). Use semantic line breaks and name the file after the issue number or the PR #.

[AdamGold]

What custom exception do you think I should raise when the return code from the command is non zero (==failed)?

[frostming]

Changes to vendors should be submitted to upstream as well.