Cmds {install,wheel} should return proper error code

The `pip` executable was returning a successful status code (`0`) when
trying to install new packages with existing previous build directories.
Cmds {install,wheel} should return proper error code

The `pip` executable was returning a successful status code (`0`) when
trying to install new packages with existing previous build directories.

Conflicts:
	tests/functional/test_install_cleanup.py
	tests/functional/test_wheel.py
authors and changelog update
Merge pull request #1162 from clarete/develop

Cmds {install,wheel} should return proper error code
merge from 1.4.X