Change GOPATH from gerrit.opencord.org to github.com/opencord

Ran `go fmt` which did some line reordering after this change

Conformed Makefile to template the imagename and use correct DOCKER_*
build variables

Change-Id: I52734e805698b305cf64eb9238b08f152f68ffd4
diff --git a/Dockerfile b/Dockerfile
index b57fadc..61933f8 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -31,7 +31,7 @@
  && go get -v github.com/grpc-ecosystem/grpc-gateway/protoc-gen-grpc-gateway \
  && go get -v github.com/golang/protobuf/protoc-gen-go
 
-WORKDIR /go/src/gerrit.opencord.org/voltha-bbsim
+WORKDIR /go/src/github.com/opencord/voltha-bbsim
 ENV GO111MODULE=on
 ENV GOPROXY=https://proxy.golang.org
 
@@ -69,6 +69,6 @@
 && touch /var/lib/dhcp/dhcpd.leases
 
 WORKDIR /app
-COPY --from=builder /go/src/gerrit.opencord.org/voltha-bbsim/bbsim /app/bbsim
+COPY --from=builder /go/src/github.com/opencord/voltha-bbsim/bbsim /app/bbsim
 
 CMD [ '/app/bbsim' ]