Clean routers in DvrRoutersNegativeTestExtended

It completes the initial patch "Add tempest tests for DVR router state
management" which doesn't clean 2 routers [1].

[1] https://review.opendev.org/#/c/668760/

Change-Id: Iec14343578ca587143a55bbd3d602790730d31b6
Signed-off-by: Cédric Ollivier <ollivier.cedric@gmail.com>
1 file changed