Run Travis CI only on selected branches, remove sudo flag
Run Travis CI only on selected branches, remove sudo flag

As we have moved the checks to prow presubmits we do not want to run the
Travis builds on PRs against master any more.

Also remove sudo flag as it has no effect for quite a while now:
https://blog.travis-ci.com/2018-11-19-required-linux-infrastructure-migration

Signed-off-by: Daniel Hiller <88b10a48ec9ada3cffd78fd3aa639ce735650d08@gmail.com>

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