Add description to Ginkgo test expectations

[peanball]

haproxy-boshrelease uses ginkgo for its acceptance tests.

Ginkgo allows adding an optional description to the Expect() statement chain, e.g.

Expect(err).ShouldNot(HaveOccurred(), "no error when starting the bosh deployment")

This helps quickly identify issues in acceptance tests without having to go to the code line, because without the description the logs say "error should not have occurred". Without context it's hard to know, which error that was exactly.