Update gopsutil godep dependency. Dont use godep go build anymore

godep seems to have a problem when dependencies have `internal`
packages. So removing `godep go build` and `godep go test` from the
build process in favor of just checking out the correct revisions using
`godep restore` into the regular GOPATH.

This basically means that we are not actually using anything within the
Godeps directory except Godeps.json. I should probably make a separate
go dependency management system that does this.

circle.yml

@@ -10,6 +10,8 @@ machine:
     - go version
 
 dependencies:
+  cache_directories:
+    - "~/telegraf-build/src"
   override:
     - docker info