IVGCVSW-3541 Change the makefiles to generate the necessary test files

IVGCVSW-3541 Change the makefiles to generate the necessary test files
for dynamic backends

 * Added dummy files and directories to use for the dynamic backend
   unit tests
 * Created a combination of valid/invalid files, valid/invalid directories
   and valid/invalid symlinks to cover all the use cases
 * Provides a base on top of which to rebase further changes for the
   developemnt of the dynamic backend feature

Change-Id: I6e157d8ba035d7931c9ea20f70ffd5b76d03334e
Signed-off-by: Matteo Martincigh <matteo.martincigh@arm.com>