Improve child process spawning

[RaeesBhatti]

- Summary
If the path to binary is not quoted on Windows and contains a space, it will get the path wrong and fail. This change makes sure that the path to app binary is quoted.
Fixes: #817

- Test plan

• Have your app binary in path with spaces
• Run netlify dev

- Description for the changelog
Quote app binary path before spawning it.

- A picture of a cute animal (not mandatory but encouraged)
🐬

[ehmicky]

Note: an alternative would be not to use shell: true. This means users won't be able to use shell features like $variable expansion or globbing, but it also means no escaping issues. It also is safer. See more information.

[RaeesBhatti]

Thanks for the tip @ehmicky. I attempted that yesterday but could make the addons tests work on Windows. Found out the problem today, we were trying to invoke a JS file without shell, which isn't supported. Updated now. Please take another look!

[ehmicky]

Is it possible for settings.command to ask for interactive input from the user?
If so, stdio: 'pipe' would not work.

[RaeesBhatti]

How about we do process.stdin.pipe(ps.stdin)?

[RaeesBhatti]

Implemented here: #823