Use the Client's http object when talking to google-resumable-media

[dhermes]

This is intended to be done after #3674. Currently, in the two places google-resumable-media is used:

$ git grep -l resumable_media -- '*/google/*'
bigquery/google/cloud/bigquery/table.py
storage/google/cloud/storage/blob.py

we manually create a transport every time the upload/download APIs are invoked (storage and bigquery).