duplication operation for cleanup resources causes fake log errors.

[SHI Peiqi]

Both rally.plugins.openstack.context.network.networks and rally.plugins.openstack.cleanup.manager try to delete network resources. which causes errors.

while rally is a project for testing, it is important to generate correct and clear log information.
fake log info will lead openstacker to bad direction and waste time.

log informations:
http://paste.openstack.org/show/497010/

[Piyush (pirsriva)]

Duplicate of https://bugs.launchpad.net/rally/+bug/1570920

[SHI Peiqi (uestc-shi)]

I am sorry, I dont understand why you marked it as a duplication, because I think I have reported it earlier and I am almost closed it.

By the way, where are you. if you have not started, I advice you to assigne to me. In this way, the community can benefit our work earlier.