Summary:The packager url for the persistent connection relied on a port
in the bundleURL, so we need to insert a sensible default. Otherwise,
issues occur: https://github.com/facebook/react-native/issues/6581
Reviewed By: bestander
Differential Revision: D3113034
fb-gh-sync-id: 4eac52631ad7abd343b75a4488bb591b5caf2145
fbshipit-source-id: 4eac52631ad7abd343b75a4488bb591b5caf2145