Remove dockerhub-related travis jobs and credentials
Remove dockerhub-related travis jobs and credentials

Signed-off-by: Federico Gimenez <85845bb0a37e1ff1f43f6c6b08d85d68227dc4c7@redhat.com>

kubevirt/kubevirt,kubevirt/kubevirt,davidvossel/kubevirt,stu-gott/kubevirt,stu-gott/kubevirt,davidvossel/kubevirt,davidvossel/kubevirt,kubevirt/kubevirt,davidvossel/kubevirt,stu-gott/kubevirt,stu-gott/kubevirt,kubevirt/kubevirt