#319 Fix Build Process

[WGierke]

I ran into a few errors while trying to build the master on Travis:

• Installing docker-engine errored with The command "sudo apt-get --force-yes -qqy -o Dpkg::Options::="--force-confdef" -o Dpkg::Options::="--force-confold" install docker-engine=17.05.0~ce-0~ubuntu-trusty" failed and exited with 100 Upgrading to Ubuntu 18 on Travis solved that and allows to use a pre-installed docker-compose.

• Next, the generated base docker containers did not provide Python 3.6. Using Ubuntu 18.04 and installing Python 3.6 first solved that.

• While installing tzdata, user interaction is needed. Adding ENV DEBIAN_FRONTEND=noninteractive solves that.

• I added git to the docker containers since npm needs that:

  npm ERR! Error while executing:
  npm ERR! undefined ls-remote -h -t ssh://git@github.com/eligrey/FileSaver.js.git
  npm ERR! 
  npm ERR! undefined
  npm ERR! No git binary found in $PATH
  npm ERR! 
  npm ERR! Failed using git.
  npm ERR! Please check if you have git installed and in your PATH.

• The refactored string interpolation in ed2c8a7bec7ce5326fdf3a5b8fbaac48facdc066 did not add leading zeroes:

  >>> n = 5
  >>> "TEST-SERIES-{:4d}".format(n)
  'TEST-SERIES-   5'
  >>> "TEST-SERIES-{:04d}".format(n)
  'TEST-SERIES-0005'

• There was a missing migration:

  +docker-compose -f local.yml run interface python manage.py makemigrations --dry-run --check
  Starting concept-to-clinic_postgres_1_61466b65a243 ... 
  Starting base                                      ... 
  /usr/local/lib/python3.6/dist-packages/environ/environ.py:618: UserWarning: Error reading /app/.env - if you're not configuring your environment separately, check this.
  "environment separately, check this." % env_file)
  Migrations for 'images':
  backend/images/migrations/0006_auto_20191203_1110.py
  - Change Meta options on imagefile

• flake8 failed due to unused variables:
  prediction/src/preprocess/lung_segmentation.py:118:5: F841 local variable '_' is assigned to but never used

• flake8 labeled an escaping \ for a RegEx string as invalid escape sequence. Changing the string to a RegEx string solved that

Proof: Succeeding build

CLA

• [x] I have signed the CLA; if other committers are in the commit history, they have signed the CLA as well