travis: switch from trusty to xenial
    
    This should fix the timeout in test-event
    
    Taken from: b635e4ef6b2f35f07111bb66a68fe850a2ccab72
    
    Resolves: #1683319
    
    patch_name: 0188-travis-switch-from-trusty-to-xenial.patch
    present_in_specfile: true
    location_in_specfile: 188
    squash_commits: true