Display progress when running with Docker

[rhigman]

When running obp-loader with Python, progress bars are displayed to show the outcome of each subprocess executed, e.g.:

$ python3 obp-loader.py 10.11647/obp.XXXX
Executing: `python3 main.py /tmp/XXXX -c bibliography-first-para bibliography-other-para -i https://doi.org/10.11647/obp.XXXX.01`
Extract the citations |################################| 2/2
Process the citations |################################| 38/38
Write to repository   |################################| 38/38
Executing: `python3 main.py /tmp/XXXX -c bibliography-first-para bibliography-other-para -i https://doi.org/10.11647/obp.XXXX.02`
Extract the citations |################################| 2/2
Process the citations |################################| 20/20
Write to repository   |################################| 20/20

When running with Docker, the subprocesses are silent:

$ docker run --rm openbookpublishers/cit-ex-obp-loader obp-loader.py 10.11647/obp.XXXX
Executing: `python3 main.py /tmp/XXXX -c bibliography-first-para bibliography-other-para -i https://doi.org/10.11647/obp.XXXX.01`
Executing: `python3 main.py /tmp/XXXX -c bibliography-first-para bibliography-other-para -i https://doi.org/10.11647/obp.XXXX.02`

This makes it difficult to tell whether any citations have actually been found and/or written to Thoth (in the event that there are no citations, the progress bars aren't shown within Python because they're triggered inside for loops).

(Note that when using --dry-run, the progress bars also don't appear within Python. Unclear whether this is a separate bug.)