Support entry point paths with spaces

[nsoranzo]

Before this patch:

$ virtualenv --version
virtualenv 20.0.6.dev5+g9201422 from /usr/users/ga002/soranzon/software/nsoranzo_virtualenv/.venv/local/lib/python2.7/site-packages/virtualenv/__init__.pyc
$ virtualenv 'foo bar'
created virtual environment CPython2.7.17.final.0-64 in 403ms
  creator CPython2Posix(dest=/usr/users/ga002/soranzon/software/nsoranzo_virtualenv/foo bar, clear=False, global=False)
  seeder FromAppData(download=False, pip=latest, setuptools=latest, wheel=latest, via=copy, app_data_dir=/usr/users/ga002/soranzon/.local/share/virtualenv/seed-v1)
  activators PythonActivator,CShellActivator,FishActivator,PowerShellActivator,BashActivator
$ head -n 3 foo\ bar/bin/pip
#!/bin/sh
'''exec' /usr/users/ga002/soranzon/software/nsoranzo_virtualenv/foo bar/bin/python "$0" "$@"
' '''
$ ./foo\ bar/bin/pip
./foo bar/bin/pip: 2: exec: /usr/users/ga002/soranzon/software/nsoranzo_virtualenv/foo: not found

After this patch:

$ virtualenv 'foo bar'
created virtual environment CPython2.7.17.final.0-64 in 336ms
  creator CPython2Posix(dest=/usr/users/ga002/soranzon/software/nsoranzo_virtualenv/foo bar, clear=False, global=False)
  seeder FromAppData(download=False, pip=latest, setuptools=latest, wheel=latest, via=copy, app_data_dir=/usr/users/ga002/soranzon/.local/share/virtualenv/seed-v1)
  activators PythonActivator,CShellActivator,FishActivator,PowerShellActivator,BashActivator
$ head -n 3 foo\ bar/bin/pip
#!/bin/sh
'''exec' "/usr/users/ga002/soranzon/software/nsoranzo_virtualenv/foo bar/bin/python" "$0" "$@"
' '''
$ ./foo\ bar/bin/pip

Usage:
  pip <command> [options]
...

N.B.: virtualenv <20 was also quoting the path and therefore did not have the issue.

Thanks for contributing a pull request, see checklist all is good!

• wrote descriptive pull request text
• added/updated test(s)
• updated/extended the documentation
• added news fragment in docs/changelog folder

[gaborbernat]

Hello, a fix for this issue has been released via virtualenv 20.0.6; see https://pypi.org/project/virtualenv/20.0.6/ (https://virtualenv.pypa.io/en/latest/changelog.html#v20-0-6-2020-02-26) . Please give a try and report back if your issue has not been addressed; if not, please comment here, and we'll reopen the ticket. We want to apologize for the inconvenience this has caused you and say thanks for having patience while we resolve the unexpected bugs with this new major release.

[soomrozaid]

I am experiencing this issue in version 20.14.1