Run 'go vet' on every commit

Also include the necessary fixes for our code to pass 'go vet' today. We can't
pass golint without a bit more work, so I'll leave it at this for a bit.

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Merge pull request #98 from tych0/go-vet

Run 'go vet' on every commit