Exit non-zero when ipython is given a file path to run that doesn't exist

[jpotter]

Simple PR to update the exit code for ipython when given a file that doesn't exist from 0 ("success") to 2 (matches python's behavior for this condition).

Currently, running ipython with a file argument that does not exist causes a zero exit code. This can cause problems in automation, i.e. bash scripts that have -e set and have an invalid file path.

$ ./venv/bin/ipython no-such-file.py
[TerminalIPythonApp] WARNING | File not found: 'foo.py'
$ echo $?
0

This PR changes the behavior to:

$ ./venv/bin/ipython no-such-file.py
[TerminalIPythonApp] WARNING | File 'no-such-file.py' doesn't exist
$ echo $?
2

[Carreau]

Thanks, that seem reasonable,