Fix makefile

Extends #264 and make Makefile targets more independent.
Now the only target which actually needs godep (cli) is `bump-deps`, `bump-deps` may be used to update dependencies and then vendoring it to Godeps directory.

All other target will either use vendored dependencies, or fetch those dependencies via `go get`, hence there's no need to separately vendor go.rice. By manipulating $GOPATH we can just install go.rice from Godeps directory.

Also enable handler testing.