Extension can hang while checking Python version

[alcarney]

[client] Python extension is available
[client] Activating python extension
[client] Running Command: /.../bin/python -c import sys ; print("{0.major}.{0.minor}.{0.micro}".format(sys.version_info))

If this command fails (such as when the configured Python does not exist), then the extension will hang as the error is not appropriately handled

[lextm]

A separate but related topic is that I found promisify(child_process.execFile) a ridiculous wrapper that cannot throw critical errors out (if you happen to quote the last parameter as "import .....". Pretty sad that it is not a reliable way yet to perform just the essential tasks like spinning out another process.

[alcarney]

This will no longer be an issue when the VSCode extension hits v1.0
See #609 for more details