[Feature request] Make network selection in entropy test configurable

If a setup with internet and internal network the test fails if the IP gets allocated from the wrong pool.

We temporarily fixed this by changing the used external network:

diff --git a/Tests/iaas/scs_0101_entropy/entropy_check.py b/Tests/iaas/scs_0101_entropy/entropy_check.py
index 47de3db..e97cdaf 100644
--- a/Tests/iaas/scs_0101_entropy/entropy_check.py
+++ b/Tests/iaas/scs_0101_entropy/entropy_check.py
@@ -197,7 +197,7 @@ class TestEnvironment:
                     "More than one external network found: "
                     + ', '.join([n.id for n in external_networks])  # noqa: W503
                 )
-            external_gateway_net_id = external_networks[0].id
+            external_gateway_net_id = external_networks[1].id
             logger.debug(f"Using external network {external_gateway_net_id}.")
             self.router = self.conn.create_router(
                 ROUTER_NAME, ext_gateway_net_id=external_gateway_net_id,

I think the name of the used network should be something configurable.