ci: disable timeout
    
    There is a bug in jenkins [1] which causes to include the time a job is
    waiting for an available executor is added to the complete execution time.
    As a consequence a job may time out without actually started because it
    did not get the executor in time.
    
    Therefore we disable the timeout completely. We can abort it manually if
    a job hangs for some reason. The job always finished so far but many jobs
    were aborted because they were waiting for an executor for a long time.
    
    [1] https://issues.jenkins-ci.org/browse/JENKINS-46569
    
    Reviewed-by: Alexey Tikhonov <atikhono@redhat.com>