Removes leftover self.conf from isolated creds

Partially implements bp config-cleanup

Change-Id: I069fd68eae3998c62efd144e1d5a44ca185e3511
diff --git a/tempest/common/isolated_creds.py b/tempest/common/isolated_creds.py
index 146fac9..ac8b14f 100644
--- a/tempest/common/isolated_creds.py
+++ b/tempest/common/isolated_creds.py
@@ -36,7 +36,6 @@
         self.isolated_net_resources = {}
         self.ports = []
         self.name = name
-        self.config = CONF
         self.tempest_client = tempest_client
         self.interface = interface
         self.password = password