Added manager list to Ovsdb Node.

Added manager list to Ovsdb Node.
For application southbound plugin only give a device level view and not a connection level view.
To make net-virt cluster aware, it needs to the managers of the ovsdb server, so that
when it creates ovs bridges, it can connect them to the same controllers through OF plugin

Tests:
ovs-vsctl set-manager tcp:ip:6640
ovs-vsctl set-manager tcp:ip:6640 tcp:ip2:6640
ovs-vsctl set-manager tcp:ip:6640
ovs-vsctl del-manager

Change-Id: I8b68fef9583f4fbcc330a0e9fc239015851b3f7c
Signed-off-by: Anil Vishnoi <vishnoianil@gmail.com>