rebuildSRPM task
    
    New task rebuildSRPM for srpms uploaded to koji. If policy
    'rebuild_srpm' returns True, build task will spawn rebuildSRPM task
    first to recreate SRPM with updated buildroot macros, typically 'dist'.
    Policy has access to same data as build_from_srpm and build_from_repo_id
    policies. (user_id, source, task_id, build_tag, skip_tag, target, tag)
    
    Fixes: https://pagure.io/koji/issue/1396