@Override
  public boolean createStream(StreamSpec streamSpec) {
    return inMemoryManager.initializeStream(streamSpec);
  }
Create a stream described by the spec.

@param streamSpec  The spec, or blueprint from which the physical stream will be created on the system.
@return            {@code true} if the stream was actually created and not pre-existing.
                   {@code false} if the stream was pre-existing.
                   A RuntimeException will be thrown if creation fails.
samza-core/src/main/java/org/apache/samza/system/inmemory/InMemorySystemAdmin.java