test/lib/base: Removes redundant routes from host
test/lib/base: Removes redundant routes from host

When creating a new Docker network (Linux Bridge), some routes to its
subnet will be installed in to the container host's routing table.
This routes enable containers to communicate each other through the
container host's rouging table, then causes the unexpected success of
scenario tests (e.g., ping between containers).

This patch removes the unexpected routes from the container host and
avoid this problem.

Signed-off-by: IWASE Yusuke <bb80e84cc9f5a8f01385872ee89032beb5d4eba7@gmail.com>

a16/gobgp,j-kato/gobgp,tamihiro/gobgp,a16/gobgp,fujita/gobgp,a16/gobgp,tamihiro/gobgp,a16/gobgp,fujita/gobgp,tamihiro/gobgp,tamihiro/gobgp,j-kato/gobgp,a16/gobgp,a16/gobgp,osrg/gobgp,osrg/gobgp,j-kato/gobgp,osrg/gobgp,osrg/gobgp,a16/gobgp,fujita/gobgp,fujita/gobgp