Make the non ha router usage explicit in a dvr test

Neutron has a non dvr, ha mode which can be a default (by
 l3_ha = True) option for all router creation.

test_centralized_router_update_to_dvr admin test case
needs to define an additional option in order to
get a `legacy` non ha router in the initial step.

Change-Id: Ib262f32133aae50cdb01d2489830499fb5c30f44
1 file changed