Speed up tests on policy-api

Test initialization and shutown of h2 database and REST server only done
once at beginning of all API unit tests. Duplicate tests removed, all
test done to persistent database and other minor improvements.

We need to check coverage after this review, ti may have dropped by a
few percent. We should design new tests to bring the coverage back up
again.

Issue-ID: POLICY-2297
Change-Id: I7ccb9835e01e08c284fdc4602e3a00e946b5e902
Signed-off-by: liamfallon <liam.fallon@est.tech>