Fault tree analysis always saves the resulting tree

[reteprelief]

We should have a method that does not save into a file. Saving can be done without depending on OsateResourceUtil and EcoreUtil for the URI. Just get the resource and its URI and for saving no need to check for the presence of folders.
needed by #1372

[lwrage]

Tests should run without a workspace. To implement that we need such a method, too.