Move ARGs to prevent invalidating docker caches

Having the ARG at the top of the dockerfiles
cause all the cached layers below to be invalidated
resulting in needlessly re-downloading or re-copying
files

Change-Id: Ie701b1556ee21ecdcf629e06c9b26d80af0fb344
diff --git a/docker/Dockerfile.simulated_onu b/docker/Dockerfile.simulated_onu
index 921fc2a..911bd4d 100644
--- a/docker/Dockerfile.simulated_onu
+++ b/docker/Dockerfile.simulated_onu
@@ -17,13 +17,6 @@
 
 FROM golang:1.12-alpine3.9 AS build-env
 
-ARG org_label_schema_version=unknown
-ARG org_label_schema_vcs_url=unknown
-ARG org_label_schema_vcs_ref=unknown
-ARG org_label_schema_build_date=unknown
-ARG org_opencord_vcs_commit_date=unknown
-ARG org_opencord_vcs_dirty=unknown
-
 # Install required packages
 RUN apk add --no-cache wget git make build-base protobuf protobuf-dev
 
@@ -46,6 +39,13 @@
 COPY adapters/common ./adapters/common
 COPY adapters/*.go ./adapters/
 
+ARG org_label_schema_version=unknown
+ARG org_label_schema_vcs_url=unknown
+ARG org_label_schema_vcs_ref=unknown
+ARG org_label_schema_build_date=unknown
+ARG org_opencord_vcs_commit_date=unknown
+ARG org_opencord_vcs_dirty=unknown
+
 # Build
 RUN cd adapters/simulated_onu && go build -o /build/simulated_onu \
 	-ldflags \