move the yum priority utility to hosts/util

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
add tests for the modifications of the utility

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
remove the utility for yum plugin priorities

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
use the new utility properly in fedora

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
properly import the pkg_managers

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
Merge pull request #237 from alfredodeza/9138

fedora should get the yum priorities plugin installed