Updating onos-prep-karaf: sed works on Mac and Linux

Change-Id: I54a5e21a72fc00277da4fc48f2b55f678c76d6db
diff --git a/tools/package/onos-prep-karaf b/tools/package/onos-prep-karaf
index 337b4b2..658c8d2 100755
--- a/tools/package/onos-prep-karaf
+++ b/tools/package/onos-prep-karaf
@@ -26,8 +26,9 @@
     $KARAF_DIR/etc/org.ops4j.pax.logging.cfg
 
 # Patch-in proper Karaf version into the startup script
-sed -i '' "s/apache-karaf-\$KARAF_VERSION/$KARAF_DIR/g" bin/onos-service
-sed -i '' "s/apache-karaf-\$KARAF_VERSION/$KARAF_DIR/g" bin/onos-client
+sed -i.bk "s/apache-karaf-\$KARAF_VERSION/$KARAF_DIR/g" bin/onos-service
+sed -i.bk "s/apache-karaf-\$KARAF_VERSION/$KARAF_DIR/g" bin/onos-client
+rm -f *.bk
 mv bin/onos-client bin/onos
 chmod a+x bin/onos-service bin/onos