net-test: build_rootfs.sh support for i386 & armhf

Bug: 126465735
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I63b719e252dde32be3996a6c9747d116650c6b7e
diff --git a/net/test/build_rootfs.sh b/net/test/build_rootfs.sh
index 887e746..72e9598 100755
--- a/net/test/build_rootfs.sh
+++ b/net/test/build_rootfs.sh
@@ -20,7 +20,7 @@
 SCRIPT_DIR=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd -P)
 
 usage() {
-  echo -n "usage: $0 [-h] [-s wheezy|stretch] [-a amd64|arm64] "
+  echo -n "usage: $0 [-h] [-s wheezy|stretch] [-a i386|amd64|armhf|arm64] "
   echo "[-m http://mirror/debian] [-n net_test.rootfs.`date +%Y%m%d`]"
   exit 1
 }
@@ -46,11 +46,15 @@
       fi
       ;;
     a)
-      if [ "$OPTARG" != "amd64" -a "$OPTARG" != "arm64" ]; then
-        echo "Invalid arch: $OPTARG" >&2
-        usage
-      fi
-      arch=$OPTARG
+      case "${OPTARG}" in
+        i386|amd64|armhf|arm64)
+          arch="${OPTARG}"
+          ;;
+        *)
+          echo "Invalid arch: ${OPTARG}" >&2
+          usage
+          ;;
+      esac
       ;;
     m)
       mirror=$OPTARG