[packagekit] mediarepo in yumbackend

[muayyad.alsadi at ojuba.org]

I have committed devicekit implementation but I have not make it the
default one

as you now the yum-backend works as non-console root and policykit won't
allow it to mount the media

a quick solution in fedora part is to add an exception for root in 

/usr/share/PolicyKit/policy/org.freedesktop.devicekit.disks.policy

or make the mounting part done by the console user as the patch I did for
yumex-nextgen