Scenario should detect tenant's network in tenant isolation mode instead of creating a new one

[Yair Fried]

Scenario tests usually create a private tenant network. In isolated_creds mode such network already exist so:
1. creating an extra network is redundant
2. it changes the network setup from what was intended when writing the test. Could be an issue for some tests
3. it consumes at least twice as much resources (ie quotas, vlans, ips)

scenrio tests should attempt to detect tenant's network in isolated_cred mode instead of creating a new network.

I'm not sure if this should be solved per test or on a global scale, and how, so I'm listing tests that are affected by this

1. scenario/test_network_basic_ops
2. sceanrio/test_cross_tenant_connectivity

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/85684

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/85684
Committed: https://git.openstack.org/cgit/openstack/tempest/commit/?id=764610afe0e269879df04f1e38795c6f8d8eb8e3
Submitter: Jenkins
Branch: master

commit 764610afe0e269879df04f1e38795c6f8d8eb8e3
Author: Yair Fried <email address hidden>
Date: Mon Apr 7 12:17:05 2014 +0300

    Disable isolated_creds.net_resources on network scenarios

    These tests creates their own network resources as part of the scenario.
    isolated_creds network resources are redundant.

    Change-Id: Iea047c48e9b50c9dcca4c73073056274594c42fb
    Partial-Bug: 1263635