selftests/functional: Add output tests

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
.travis.yml: Install C toolchain in Travis's VM

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #87 from avocado-framework/doublefree-functional

Doublefree functional