pip silently fails to install extras and returns error code

It seems that pip just returns success code on anything related to use of extras, commands like: pip install -e .[non_exiting_extra] reports success.

Even worse, with existing extras that may fail to install, the final result code is still a success, when in fact pip failed to install dependencies.

This is a critical bug because it directly affect CI usage where we can no longer trust result code from pip, bugs may go in unnoticed.