Added Drupal update check

[rimi-itk]

Adds a check to check that site can be updated (after a clean installation using the base ref).

We're pragmatic and still allow breaking changes, but in the future we have to make sure that we have a clean update path for our projects.

Example on breaking the update path:

git checkout 9d368a5724bd2c94ccb8c5703bb3d8f558a70a3f
task site-install --yes

git checkout 6a563c55dcbe1397487aea08764450ef8e67784e
task site-update --yes