Mypy failures are silenced.

[ericsnowcurrently]

When mypy fails (e.g. when .py filename contains illegal characters) the extension acts as though nothing bad happened and as though the checked files are free of problems (even if there are some). It shouldn't be failing silently.

To reproduce:

1. set the current workspace to use mypy
2. add a file with an invalid filename
3. add code that would cause mypy to report problems
4. save it (triggering mypy to run
5. check the "Problems" pane (no problems reported)

If you set "python.linting.mypyPath": "/bin/echo" then you'll see (in the Output pane) exactly how the extension invokes mypy. Invoking it manually using those args will show the failure output from mypy. That's what we should be showing normally rather than hiding it.

So here's what should probably be done:

• write mypy error output to "Python" output pane
• pop up a message saying that mypy failed

[karthiknadig]

This should now be addressed in the new mypy extension: https://marketplace.visualstudio.com/items?itemName=ms-python.mypy-type-checker