Change TFRUtil to TFRecorder in Notebooks

[jmarrietar]

Describe the bug
Notebooks inside samples directory have import tfrutil both from https://github.com/google/tensorflow-recorder/blob/master/samples/Basic-TFRecorder-Usage.ipynb and https://github.com/google/tensorflow-recorder/blob/master/samples/Using-TFRecorder-with-Google-Cloud-Dataflow.ipynb

To Reproduce
Steps to reproduce the behavior:

1. Go to samples directory and try to run the imports.

Expected behavior
import tfrecorder

Additional context
Maybe because this notebooks are still in an early phase. Cheers,

[mbernico]

Created hotfix 18 to address this.