[docker] Combine apt-get update with apt-get install.

Running RUN apt-get update by itself will cause it to use the cache when
rebuilding the dockerfile. This can lead to apt-get installs failing
when updating programs. The preferred method is RUN apt-get update &&
apt-get install -y <any apt-get installs you need>. this will force
apt-get update to run when any package is updated, or new ones are
installed.

https://github.com/docker/docker/issues/3313
Add beautifulsoup4 in requirements.
Merge branch 'bs4'