Add revision info to docker images' name

[BenjaminRodenberg]

Currently it is not easy to find out which code revision a docker image uses or to use a specific revision. precice/precice-ubuntu1604.home-develop, for example, might refer to any revision on develop. This becomes especially problematic, when a test fails, but it is unclear which revision certain parts of the toolchain are using.

An example implementation might be using the label of the image to identify the revision. Example: precice/precice-ubuntu1604.home-develop:9660959 will refer to an image that was built based on precice revision precice/precice@9660959. Note that for the preCICE base images the situation is relatively simple. However, if we look at the adapter images there are much more relevant pieces of information and using the tag might not be sufficient; the solution proposed in #138 might be more appropriate.

Note that this change will cause many changes in our systemtests. Therefore, I would suggest to first carefully evaluate whether it is worth it and link related issues to this one.