Bug#933578: Possible fix scanning with HP MFP that requires a plugin

I had quite some difficulty getting "hp-setup" to configure a HP Color LaserJet Pro MFP M277dw to allow scanning + "hp-toolbox" to allow scanning, status check, etc. on Debian 10.

See: https://bugs.launchpad.net/ubuntu/+source/hplip/+bug/1430561/comments/39

I found several things which together got scanning and hp-toolbox 

working for me with my HP Color LaserJet Pro MFP M277dw. I hope the proceedure below is of help to someone else.

1. Fix the source for the gpg key to avoid the problem with the pgp.mit.edu server:

   sudo cp -a /usr/share/hplip/base/validation.py /usr/share/hplip/base/validation.py.ORIG

   vim /usr/share/hplip/base/validation.py

   # replace pgp.mit.edu with pool.sks-keyservers.net on line 44

2. After getting the plugin to install using "hp-plugin" as a regular user and the root password when requested, the software still complained...

3. It seems that hplip expects the libraries in a different location than where they are getting installed:

   find /usr/lib -name "*sane*" | grep hp2000S

   sudo ln -s /usr/lib /usr/lib/i386-linux-gnu

   sudo ln -s /usr/lib64 /usr/lib64/x86_64-linux-gnu

(Based on https://bugs.launchpad.net/hplip/+bug/1818629)