Protobuf files need to be regenerated because (I think) Golang 1.7.3 uses a somewhat different method of ordering fields in a struct when marshaling to bytes.
The `letsencrypt/boulder-tools` image was recently updated, pulling in version
0.8.0 of certbot. That version stores the output of `certonly` requests in a
different path. In test.sh, we check out a specific tagged release of certbot in
order to get its integration tests. Prior to this commit, we were using
certbot 0.8.0 with the integration tests from version 0.6.0 of certbot,
which looked for `certonly` output in the wrong place, and failed.
This commit changes test.sh to checkout the 0.8.0 branch, and also removes a
temporary shim we used to make the `certbot` command call out to the
`letsencrypt` command.
Also, since the latest version of `letsencrypt/boulder-tools` includes an updated
`protoc-gen-go`, this change also updates the support packages to match.