inconsistent pipenv behaviour with symlinked directory and PIPENV_PIPFILE

[pbadenski]

Issue description

When pipenv is run with PIPENV_PIPFILE and pointing to a directory that is a symlink, .venv location is not resolved correctly.

Expected result

Running:

cd DIR
pipenv --venv

and

PIPENV_PIPFILE=DIR/Pipfile pipenv --venv

and

PIPENV_PIPFILE=$(readlink -f /root/kaa/Pipfile) pipenv --venv

should all give the same output if DIR is a symlink.

Actual result

# ls -la kaa
lrwxrwxrwx 1 root root 27 Jan 28 06:23 kaa -> /root/kaa-2020-01-28-062244

# PIPENV_PIPFILE=/root/kaa/Pipfile pipenv --venv
/root/.local/share/virtualenvs/kaa-E5w9dr-j

# PIPENV_PIPFILE=$(readlink -f /root/kaa/Pipfile) pipenv --venv
/root/.local/share/virtualenvs/kaa-2020-01-28-062244-UsgZQKBN

# cd kaa
~/kaa# pipenv --venv
/root/.local/share/virtualenvs/kaa-2020-01-28-062244-UsgZQKBN