tests: fix race condition on archive policies

In some cases, one of the test might be creating the policies while the
other test is getting an error and trying to fetch them. But it might be
that the first test didn't finished to create all tests:

T1: create high policy -> OK
T2: create high policy -> KO
T2: get high policy -> OK
T2: get medium policy -> KO -> test fails!
T1: create medium policy -> OK

Let's fix that by creating or getting one policy at a time.

Change-Id: I5e4006decb9f8c50cb8d54d9f90c0ecdbd875a63
Merge "tests: fix race condition on archive policies"