to not keep old debs for experimental

Signed-off-by: Jessica Frazelle <acidburn@docker.com>

hack/make/release-deb

@@ -38,6 +38,7 @@ fi
 # set the component and priority for the version being released
 component="main"
 priority=700
+options="--keepunreferencedfiles"
 
 if [[ "$VERSION" == *-rc* ]]; then
 	component="testing"
@@ -47,6 +48,7 @@ fi
 if [ $DOCKER_EXPERIMENTAL ] || [[ "$VERSION" == *-dev ]] || [ -n "$(git status --porcelain)" ]; then
 	component="experimental"
 	priority=600
+	options=
 fi
 
 # release the debs
@@ -64,7 +66,7 @@ for dir in contrib/builder/deb/*/; do
 			-k releasedocker --sign builder "${DEBFILE[@]}"
 	fi
 
-	reprepro -v --keepunreferencedfiles \
+	reprepro -v $options \
 		-S docker-engine -P "$priority" -C "$component" \
 		-b "$APTDIR" includedeb "$codename" "${DEBFILE[@]}"
 done