Install configs into /etc, not /usr/etc

Not providing an absolute path to data_files means that "setup.py
install" will put it under whatever "--prefix" is specified. For most
RPM-based distros this is /usr. For machine-local installations this is
/usr/local. However, there's no such thing as /usr/etc or
/usr/local/etc, there's just /etc.

Distributions could either fix this manuall or work-around by using
"python setup.py --install-data=/etc". But this isn't future-proof since
all data would end up in the (potentially) wrong place.

Change-Id: I844b33d1fdd87f2c255f72b30a78eeab677ec09d
Merge "Install configs into /etc, not /usr/etc"