Improve the provisioning script sha1 computation in storage

Problem outline

We have a common folder in qt/qt5.git repository for provision scripts that creates cross-dependencies between different platforms. This results in the following:

• Changing a provisioning script in common folder will force re-provisioning of all machines (waste of resources and makes us vulnerable for re-provisioning fails)
• If a commit introduces a bug in a common provision script, this will break provisioning for all the platforms that use that common file (worst case scenario)
• Developers in my team are afraid to touch the files in the common folder (slows down development)