.gitlab-ci.yml: Fix and refactor the whole pipeline

.gitlab-ci.yml

-# Use a debian image with python 3.5 (and pip3) pre-installed
+# Debian Stretch base image with python 3.5:
+#
 image: python:3.5-stretch
 
-variables:
-  BGD: bgd
-
 stages:
   - test
   - post
   - deploy
 
 
-before_script:
-  - python3 -m pip install --upgrade setuptools pip
-  - export PATH=~/.local/bin:${PATH}
-  - python3 -m pip install --user --editable ".[tests]"
+# Templates and global variables.
+#
+variables:
+  BGD: "${CI_PROJECT_DIR}/env/bin/bgd"
+  PYTHON: "${CI_PROJECT_DIR}/env/bin/python"
+
+.build-template:
+  before_script: &install-base
+    - /usr/bin/python3 -m venv env  # Creates a virtual environment
+    - ${PYTHON} -m pip --cache-dir=.pip install --upgrade setuptools pip wheel
+    - ${PYTHON} -m pip --cache-dir=.pip install --editable ".[auth,docs,tests]"
+  cache:
+    paths:
+      - .pip
+
 
-.tests-template: &linux-tests
+# Test stage, build and test the code.
+#
+unit-tests:
   stage: test
-  variables:
-    PYTEST_ADDOPTS: "--color=yes"
+  extends: .build-template
   script:
-    - python3 -m pip install --user --editable ".[auth]"
-    - python3 setup.py test
+    - ${PYTHON} setup.py test
+  after_script:
     - mkdir -p coverage/
     - cp .coverage coverage/coverage."${CI_JOB_NAME}"
+  variables:
+    PYTEST_ADDOPTS: "--color=yes"
   artifacts:
     paths:
-    - coverage/
+      - coverage/
 
-.run-dummy-job-template: &dummy-job
+dummy-tests:
   stage: test
+  extends: .build-template
   script:
     - ${BGD} server start data/config/default.conf &
-    - sleep 1 # Allow server to boot
+    - sleep 1  # Allows server to boot
     - ${BGD} bot dummy &
     - ${BGD} cas upload-dummy
     - ${BGD} execute request-dummy --wait-for-completion
 
-
-# Test stage, build and test the code.
-#
-tests-debian-stretch:
-  <<: *linux-tests
-
-run-dummy-job-debian:
-  <<: *dummy-job
-
-buildbox-e2e:
-  image: registry.gitlab.com/buildgrid/buildbox/buildbox-e2e:latest
+e2e-tests:
   stage: test
-  before_script: []
+  image: registry.gitlab.com/buildgrid/buildbox/buildbox-e2e:latest
   script:
     - BUILDGRID_SOURCE_ROOT=`pwd` end-to-end-test.sh
 
+
 # Post-build stage, documentation, coverage report...
 #
 documentation:
   stage: post
+  extends: .build-template
   script:
     - apt-get update && apt-get install -y graphviz
-    - python3 -m pip install --user --editable ".[docs]"
     - make -C docs html
     - mkdir -p documentation/
     - cp -a docs/build/html/. documentation/
   artifacts:
     paths:
-    - documentation/
+      - documentation/
 
 coverage:
   stage: post
+  extends: .build-template
   dependencies:
-  - tests-debian-stretch
+    - unit-tests
   coverage: '/TOTAL +\d+ +\d+ +(\d+\.\d+)%/'
   script:
-    - python3 -m pip install --user --editable ".[tests]"
-    - cd coverage/
-    - ls -l .
-    - python3 -m coverage combine --rcfile=../.coveragerc --append coverage.*
-    - python3 -m coverage html --rcfile=../.coveragerc --directory .
-    - python3 -m coverage report --rcfile=../.coveragerc --show-missing
-    - python3 -m coverage erase --rcfile=../.coveragerc
+    - cd coverage/ && ls -la .
+    - ${PYTHON} -m coverage combine --rcfile=../.coveragerc --append coverage.*
+    - ${PYTHON} -m coverage html --rcfile=../.coveragerc --directory .
+    - ${PYTHON} -m coverage report --rcfile=../.coveragerc --show-missing
+    - ${PYTHON} -m coverage erase --rcfile=../.coveragerc
   artifacts:
     paths:
-    - coverage/
+      - coverage/
 
 # Deployement stage, only for merges which land on master branch.
 #
 pages:
   stage: deploy
   dependencies:
-  - coverage
-  - documentation
+    - coverage
+    - documentation
   script:
-  - mkdir -p public/coverage/
-  - cp -a coverage/* public/coverage/
-  - ls -la public/coverage/
-  - cp -a documentation/* public/
-  - ls -la public/
+    - mkdir -p public/coverage/
+    - cp -a coverage/* public/coverage/
+    - ls -la public/coverage/
+    - cp -a documentation/* public/
+    - ls -la public/
   artifacts:
     paths:
-    - public/
+      - public/
   only:
-  - master
+    - master
 
-trigger-buildbox-e2e-rebuild:
+triggers:
   stage: deploy
-  variables:
-    GIT_STRATEGY: none
-  script:
+  before_script:
     - apt-get update && apt-get install -y curl
+  script:
     - curl --request POST --form "token=$CI_JOB_TOKEN" --form ref=master https://gitlab.com/api/v4/projects/buildgrid%2Fbuildbox%2Fbuildbox-e2e/trigger/pipeline
+  variables:
+    GIT_STRATEGY: none
   only:
     - master