CI - More aggressive caching for Drupal and NPM

[AronNovak]

Status

Started to think about the structure

Todo:

• cache Drupal source (except custom modules)
• cache NPM installs
• add invalidation logic
• tests

will fix #103

[AronNovak]

I spent 5.25 hours on this issue so far, i still have a little remaining, but likely i will run out of time here. The only thing left however is to debug. At local, using Docker Compose, I could trigger the cache use, and it worked, on Travis, it fails, it says some modules are missing, so somehow the content of the cache is unusable. Apart from this, what was planned was implemented, for both Drupal and NPM.
//cc @amitaibu

[AronNovak]

  for FILE in $(git ls-files --others -i --exclude-standard)
  do  
    cp --parents "$FILE" "$TRAVIS_CACHE_DIR"/www_ignored
  done

Tested at local Docker execution, this part is not yet effective, debugging to be continued.
ci-scripts/docker_files/post_cache.sh

[AronNovak]

The caching itself works, i cannot tell the exact numbers, but i expected a bit better improvement of execution speed.
I wanted to invite our @gizra-robot friend to post a video, as many things were changed, but waiting for zalando/zalenium#131 to be able to continue.

[gizra-robot]

• Video of the failed WebdriverIO test login.

[AronNovak]

Ready for review. The speed gain will be likely even more for real-world projects based on Elm Starter, where the drush si is slower for instance.

[AronNovak]

[amitaibu]

Lovely!