androidtest.bash: set GOARM=7

It's the only ARM version we have ever supported on android.
(Not setting it caused some builder timeouts.)

Change-Id: I26061434252ff2a236bb31d95787a1c582d24b3f
Reviewed-on: https://go-review.googlesource.com/16295Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

src/androidtest.bash

@@ -23,6 +23,14 @@ if [ "$GOOS" != "android" ]; then
 	exit 1
 fi
 
+if [ -z $GOARM ]; then
+	export GOARM=7
+fi
+if [ "$GOARM" != "7" ]; then
+	echo "android only supports GOARM=7, got GOARM=$GOARM" 1>&2
+	exit 1
+fi
+
 export CGO_ENABLED=1
 unset GOBIN