Updated _create_vif part of create tap interface with tunctl

Signed-off-by: Takaaki Suzuki <suzuki@midokura.com>
Fix wrong default value of midonet_use_tunctl

Fixes #36

Signed-off-by: Tomoe Sugihara <tomoe@midokura.com>
Merge pull request #40 from midokura/grizzly_dev

Update for midonet_use_tunctl