run mock_init in Future + init dnf sack

[jsilhan]

use Futures
DNF sack should be also Future, the repodir should be set to /etc/yum.repos.d/ in mock and cachedir should be set to /var/cache/dnf/ in mock.

[jsilhan]

it should be one commit each:

• make mock init a Future with defined end
• previous from page 2 to 1 should cancel Future (GUI)
• load dnf sack as Future mapped to mock init

[jsilhan]

#372 should replace this. QtScheduler could be probably used.

[onionka]

Will we ever need to cancel running initialization of mock and dnf? Because it cannot be done with future object (or I don't know the right way).

[jsilhan]

you don't need to deal with canceling the Future right now.