IPykernel breaking pipenv virtual env on python 3.7.2

使用 Python 3.7.2 和 issue 中的 pipenv 命令重现 Windows 失败，然后检查 traceback 中的 site-packages\win32\lib\pywin32_bootstrap.py 入口点。完成的标准是安装 ipykernel 不再破坏虚拟环境，并且之后 python 能够成功启动。

Steps to reproduce:

1. Create new pipenv environment:
   pipenv shell
2. Install ipykernel
   pipenv install ipykernel
3. Installation throws error: AttributeError: module 'site' has no attribute 'getsitepackages'
4. python.exe now doesn't work. Throws the same error:
   `> python

Fatal Python error: initsite: Failed to import the site module

Traceback (most recent call last):
File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 791, in
main()
File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 768, in main
paths_in_sys = addsitepackages(paths_in_sys)
File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 280, in addsitepackages
addsitedir(sitedir, known_paths)
File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 211, in addsitedir
addpackage(sitedir, name, known_paths)
File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 179, in addpackage
exec(line)
File "", line 1, in
File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site-packages\win32\lib\pywin32_bootstrap.py", line 14, in
for maybe in site.getsitepackages():
AttributeError: module 'site' has no attribute 'getsitepackages'`

ERROR ON CREATING NEW ENVIRONMENT:
`
Successfully created virtual environment!

Virtualenv location: C:\Users-.virtualenvs\test-gBjW7Fpf

Installing ipykernel…

Adding ipykernel to Pipfile's [packages]…

Installation Succeeded

Pipfile.lock not found, creating…

Locking [dev-packages] dependencies…

Locking [packages] dependencies…

Locking Failed!

Fatal Python error: initsite: Failed to import the site module

Traceback (most recent call last):

File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 791, in

main()

File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 768, in main

paths_in_sys = addsitepackages(paths_in_sys)

File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 280, in addsitepackages

addsitedir(sitedir, known_paths)

File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 211, in addsitedir

addpackage(sitedir, name, known_paths)

File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 179, in addpackage

exec(line)

File "", line 1, in

File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site-packages\win32\lib\pywin32_bootstrap.py", line 14, in

for maybe in site.getsitepackages():

AttributeError: module 'site' has no attribute 'getsitepackages'

Traceback (most recent call last):

File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 791, in

main()

File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 768, in main

paths_in_sys = addsitepackages(paths_in_sys)

File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 280, in addsitepackages

addsitedir(sitedir, known_paths)

File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 211, in addsitedir

addpackage(sitedir, name, known_paths)

File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site.py", line 179, in addpackage

exec(line)

File "", line 1, in

File "C:\Users-.virtualenvs\test-gBjW7Fpf\lib\site-packages\win32\lib\pywin32_bootstrap.py", line
14, in

for maybe in site.getsitepackages():

AttributeError: module 'site' has no attribute 'getsitepackages'
`