Add fixes for voltha-protos testing

Add protoc-gen-go for Go protobuf generation
Set PATH and GOPATH in python-unit template

Change-Id: Ibe92ea06e9f5f6ff4d60455a640e3f5551cbee20
diff --git a/packer/provision/basebuild.sh b/packer/provision/basebuild.sh
index 4428bff..62eebcc 100644
--- a/packer/provision/basebuild.sh
+++ b/packer/provision/basebuild.sh
@@ -183,6 +183,7 @@
     export GOPATH=/usr/local/go
     mkdir -p $GOPATH
     export PATH=$PATH:/usr/lib/go-1.10/bin:$GOPATH/bin
+
     # converters for unit/coverage test
     go get -v github.com/t-yuki/gocover-cobertura
     go get -v github.com/jstemmer/go-junit-report
@@ -195,6 +196,14 @@
       go install -ldflags="-X main.version=v0.5.0" ./cmd/dep
     popd
 
+    # protoc-gen-go - Golang protbuf compiler extension for protoc (installed
+    # below)
+    go get -d -u github.com/golang/protobuf/protoc-gen-go
+    pushd $(go env GOPATH)/src/github.com/golang/protobuf
+      git checkout "v1.3.1"
+      go install ./protoc-gen-go
+    popd
+
     # install repo
     REPO_SHA256SUM="394d93ac7261d59db58afa49bb5f88386fea8518792491ee3db8baab49c3ecda"
     curl -o /tmp/repo 'https://gerrit.opencord.org/gitweb?p=repo.git;a=blob_plain;f=repo;hb=refs/heads/stable'