unplug_interface of LinuxBridgePlugin.py references non-existing exception

[yong sheng gong]

unplug_interface of LinuxBridgePlugin.py references non-existing exception InvalidDetach.
According to plugin api of QuantumPluginBase, unplug_interface should only raise exception.NetworkNotFound
        exception.PortNotFound

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/7897

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/7897
Committed: http://github.com/openstack/quantum/commit/93ee2838a2937e346e78c2e3ee21f5fed478d66f
Submitter: Jenkins
Branch: master

commit 93ee2838a2937e346e78c2e3ee21f5fed478d66f
Author: Yong Sheng Gong <email address hidden>
Date: Wed May 30 13:59:52 2012 +0800

    Remove the reference to non existing exception by linuxbridgeplugin.

    Bug #1006221

    According to plugin api of QuantumPluginBase, unplug_interface
    should only raise exception.NetworkNotFound and exception.PortNotFound.
    To unplug a non-attached port should not raise Exception.
    After this modification, to unplug an non-attached port will have no impact.
    In addition, I remove the 'network = db.network_get(net_id)' since
     'db.validate_port_ownership(tenant_id, net_id, port_id)' statement has taken
    care of the check.

    patch 2: split test case to test it exclusively compared to patch 1.
    patch 3: remove added test statement in previous test case

    Change-Id: I437c3f13fa7a81aeabcdfca7ba03e94a0a7aa32b