Update getStreamInfo usage

[crazyzhou]

In pravega/pravega#6748, Pravega team decided to change the signature of the getStreamInfo usage, we need to update into the new API fetchStreamInfo in the connector for 0.13 version.

Suggestions
Add a new method in the helper class like

StreamInfo getStreamInfo(String scopeName, String streamName) {
    return fetchStreamInfo(scopeName, streamName).join();
}