Improve error bubbling

[martriay]

As seen in many issues as #108, when there's an upstream error in Nile (e.g. when the underlying command such as starknet or starknet-devnet fails), the output is very obscure about the reasons of the error.

Fix nile so it propagates the error message and help users troubleshoot nile.

[fracek]

I think the way to do this is by capturing the subprocess output (should we differentiate stdout and stderr with e.g. color?), capture any exception to suppress the default python stacktrace and simply inform the user something went wrong. I believe we have no way to know exactly went wrong in the subprocess to display more information about it.