Install packages from prefered repositories.

* Yyoom tries to install packages from preferred
  repositories and, if packages were not found,
  tries to install them from default ones.
* Preferred repositories are passed to yyoom from
  the dependency handler.

Change-Id: Iede5ad1c58c105c2627ad1012e959f0f93c4a447
Merge "Install packages from prefered repositories."