Refactor functional tests to create base class for agent functional tests

[Kyle Mestery]

I'm writing additional functional tests which require sudo. There is also additional shared code from some existing agent tests which would be nice to use. It makes sense to refactor the functional tests to provide a base class which all these classes can inherit from.

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.openstack.org/84856

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/84856
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=783b88ccdd2c8e9e239c5ee123841188c60e01b5
Submitter: Jenkins
Branch: master

commit 783b88ccdd2c8e9e239c5ee123841188c60e01b5
Author: Kyle Mestery <email address hidden>
Date: Wed Apr 2 14:39:13 2014 +0000

    Revert changes removing OVSBridge return

    This reverts changes from this review [1] which incorrectly removed
    the return of the OVSBridge object when calling BaseOVS.add_bridge.
    This broke all functional tests relying on this return.

    [1] https://review.openstack.org/#/c/71142/

    Related-Bug: #1301363

    Change-Id: If32e155cc2bd368b2e842f14b1d1da0827ccfeff

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/84923

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/84923
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=83a11d406eb421285a7fffd3ce853394211ac397
Submitter: Jenkins
Branch: master

commit 83a11d406eb421285a7fffd3ce853394211ac397
Author: Kyle Mestery <email address hidden>
Date: Wed Apr 2 07:17:37 2014 +0000

    Add common base class for agent functional tests

    Refactor the functional tests a bit to add a common base class for agent
    tests. This is needed an upcoming commit which adds a functional test
    for VXLAN version checking.

    Closes-Bug: #1301363

    Change-Id: I438e401cbfb40e5557e5125f2a409bac5c1fd1c2