Improve bind performance

We should keep in mind that UEPConnection.bindByEntitlementPool returns the list of entitlements bound (always len 1 in this case).  That cannot replace certlib.update because of modifier products, but if we serialize it from the json response, certlib.update will have one less serial to pull down.  That could be a bit change though, because we have to trigger the same callbacks (branding hook, repo hook etc).