cisco.l3.plugging_drivers has been moved out from neutron repo

The following commit in neutron move cisco.l3.plugging_drivers out of neutron.

commit 41166d533383e3490ffe6c2b1b200053d90e0b83
Merge: 4663a15 b6ba733
Author: Jenkins <email address hidden>
Date: Mon Mar 9 17:52:19 2015 +0000

    Merge "Vendor decomposition to move CSR1000v support to the networking-cisco repo"

but neutron-vpnaas still refer it, so the unit test failed as below:

hua@hua-ThinkPad-T440p:/bak/openstack/neutron-vpnaas$ python setup.py testr --slowest --testr-args=
running testr
running=OS_STDOUT_CAPTURE=1 OS_STDERR_CAPTURE=1 OS_LOG_CAPTURE=1 ${PYTHON:-python} -m subunit.run discover -t ./ ${OS_TEST_PATH:-./neutron_vpnaas/tests/unit} --list
--- import errors ---
Failed to import test module: neutron_vpnaas.tests.unit.services.vpn.service_drivers.test_cisco_ipsec
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/unittest2/loader.py", line 445, in _find_test_path
    module = self._get_module_from_name(name)
  File "/usr/local/lib/python2.7/dist-packages/unittest2/loader.py", line 384, in _get_module_from_name
    __import__(name)
  File "neutron_vpnaas/tests/unit/services/vpn/service_drivers/test_cisco_ipsec.py", line 27, in <module>
    from neutron_vpnaas.services.vpn.service_drivers \
  File "neutron_vpnaas/services/vpn/service_drivers/cisco_ipsec.py", line 16, in <module>
    from neutron.plugins.cisco.l3.plugging_drivers import (
ImportError: No module named l3.plugging_drivers
Non-zero exit code (2) from test listing.
error: testr failed (3)