Add GOVETFLAGS

[Stebalien]

In some cases, we're not going to be able to fix all go vet errors and may need to disable some checks. Ideally, we'd just be able to silence specific issues but, we'll, we're dealing with the go devs here.

[Kubuxu]

I still think we should use codeclimate for govet as it allows tracking specific issues (including ignoring them).

[kevina]

@Kubuxu what do I (or you) need to do to set up codeclimate?

[kevina]

@Kubuxu @Stebalien did you come to any sort of consistence on IRC?

We should resolve this issue before merging the Travis CI p.r. in case we need to somehow update the .travis.yml for this to work.

[Kubuxu]

Let's skip codeclimate.

[kevina]

Okay do we want to use GOVETFLAGS to add optional flags (see https://golang.org/cmd/vet/) or make it GOVETCMD which can include flags but also be used to disable vo-vet altogether by assigning it to true. If we go with GOVETCMD than an undefined value will default to go vet.

[Kubuxu]

SGWM.

[kevina]

GOVETCMD is now supported.