Fix command to execute on changed make.conf

emerge --changed-use @world would cause packages to be upgraded. Instead
we run emerge --changed-use on the list of installed atoms with versions
included.
Allow installing portage-utils using class portage

We use qlist from app-portage/portage-utils in this class.
Ensure dependent packages are installed by default
Merge pull request #117 from vikraman/fix/makeconf

Fix rebuild command on changed make.conf