There are use cases where an user wants to not have backend packages
automatically installed. One use case would be the user having an alternative
set of packages already providing backend packages as built-in dependencies.
Installing system packages is redundant, useless and causing confusion.
This change adds the ability to disable backend packages management
while preserving previous behavior which consists of installing them
automatically.
Closes-bug: #1715204
Change-Id: Ief676d4c5aaa81f4547dd2e090dfcc8c62855148
5911b080b3