LBaaS add missing rootwrap filter for route

If one runs the lbaas agent from packages and does not have the l3-agent
installed on the same box as the lbaas agent it will fail to add the
default gw route. This is because it's missing the rootwrap filter for
route which is only present in l3.filters.

Change-Id: I59cd0a549a1f1d1564d139d42daf55d02898bf76
Closes-bug: 1325406
Merge "LBaaS add missing rootwrap filter for route"