python:tests: Reuse policies and silos created by setUp() across all tests

We now create the claims in setUp() only once, preserving them so as to
reuse them across all of the tests using this class. Then we finally
delete them all in tearDownClass().

addClassCleanup() could make this cleaner, but it’s available only in
Python 3.8 and above.

This change reduces the time taken by my machine to run
samba.tests.samba_tool.domain_auth_policy from two minutes to ten
seconds.

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

python/samba/tests/samba_tool/domain_auth_silo.py

@@ -458,7 +458,7 @@ class AuthSiloMemberCmdTestCase(BaseAuthCmdTest):
         # Remove organisational unit.
         self.samdb.delete(self.ou, ["tree_delete:1"])
 
-        # Remove members from silos before deleting them in super.
+        # Remove members from silos.
         for silo, members in self.members.items():
             for member in members:
                 self.remove_silo_member(silo, member)