TEIIDDES-2120: Fix and add VDB unit tests

* Vdb
 * Utilise VdbConstants
 * Ensures that the full path of the vdb's file does not duplicate the
   path of the tmp folder when saving occurs

* MockFileBuilder
 * 1-stop class for mocking a path, its related IFile and underpinned by a
   real file

* VdbFileEntryTest
* VdbTest
 * Fixes tests to cope with more calls to the mocked paths
 * New tests for exploring the functionality of the vdb