register monitor_linux and monitor_openflow for VRRPInterfaceMonitor class

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
fix vrrp utils

Maybe better to split api stuff from topology/switches.py but had
better move utils.py out of vrrp directory. For now, adopt it for the
current code.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Add support for admin_state (role)

Signed-off-by: Anantha Ramaiah <ananth@ntti3.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
vrrp: add statistics support

Supports statistics that Commercial routers provides.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
vrrp: declare event.py to be dependent for manager.py

So if you start RyuApp using event.py, manager.py will be started.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>