[FIX] packages: fix docker images builds tests

The automated tests of rpm,deb and src packages are using docker
images and containers. Those tests were not working as expected due
to various small glitches:
* some debian python- packages were missing in the Debian image
* pip was called instead of pip3 for the src test
* a wrong addons path was given for the tests
* the containers id's were wrong due to a bytes implicitly converted
  to str