Fixed mash directive
    
    Summary: Mash directive created non-valid config for mash.
    
    Test Plan: unittests work and the mash directive correctly uses mash to solve multilib
    
    Reviewers: kparal, tflink
    
    Reviewed By: kparal, tflink
    
    Subscribers: tflink
    
    Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D144