Starting hp-toolbox as non-root-user to configure my printer/scanner combo
Laserjet Pro 100.
Printing works fine but scanner requires a plugin which can be downloaded and
installed from within the hp-toolbox.
hp-toolbox queries for the root password during plugin installation, but the
password is not accepted.
Apparently, Ubuntu has the same bug.
https://bugs.launchpad.net/hplip/+bug/1521006
Their workaround ( ~/.hplip/plugin_tmp/ && /usr/bin/sudo /usr/bin/python
installPlugin.py ) also works for openSUSE Leap 42.3, but it is an unnecessary
hurdle.