Allow CLI module to handle nonzero response codes without failing

Fixes https://github.com/Codeception/Codeception/issues/1603.

As explained in the issue, I wanted to test the output of a command that would return a nonzero result code. 

This change allows the `runShellCommand` function to take an optional parameter to disable the auto-failure of a test for instances where the resultcode is expected to be nonzero.