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
TEIIDDES-2120: Erroneous relativising of path value

* Seems making the path relative to the tmp folder is not a good idea
  since it adds a ../ to its beginning. This causes the createTempFile
  method to fail.

* Causes preview vdbs creation to fail with a "no such file or directory"
  error

* Originally added to stop path being a full duplication of tmpFolder,
  which occurred in some unit tests. However, this does not seem to be
  repeated so removing.