Integrated terminal with zsh shell should use Python virtualenv

[dinhkim]

Environment data

• VS Code version: 1.32.3
• Extension version: 2019.2.5558
• OS and version: Windows 10 (Build 1809)
• Python version: 3.7.2
• Type of virtual environment used: venv
• Shell of Integrated Terminal: zsh (C:\msys64\usr\bin\zsh.exe)

Expected behaviour

VS-Code integrated terminal should use the path to virtualenv python not the system default

Actual behaviour

When a virtualenv is selected, the integrated terminal (zsh) does not use the virtual environment.
However, if I use bash shell for the integrated terminal, everything is working fine.

Steps to reproduce:

1. python.pythonPath is set to virtual environment path
2. Open the integrated terminal
3. python --version in integrated terminal shows system version

[dinhkim]

I think the "src/client/common/terminal/helper.ts" file need to be updated to detect the zsh shell of msys2 on Windows.

[DonJayamanne]

Unfortunately we do not support msys2, closing in favor of #67