Test regression overwrite by newer file

* Adds regression tests for checking if newer file from blueprint B
  that is loaded after blueprint A overwrites a file from A.

Reported-by: Javier Martin Montull <javier.martin.montull@cern.ch>
Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Fixes file overwrite regression

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Merge pull request #8 from jirikuncar/fix-modification-date-check

Fix modification date check