Add method to return resource directory contents

Add method to return resource directory contents

In order to avoid hard coding the policy types and policies that are in
the example directories into unit test cases, and in order to
automatically pick up added and removed policy types and policies, it
would be good to read the contents of resource directories at run time
in unit tests. This change brings in that functionality into
ResourceUtils.

Issue-ID: POLICY-2315
Change-Id: I601718828aad0f065dbbaa1f5af8d0a0f133f44d
Signed-off-by: liamfallon <liam.fallon@est.tech>