Remove hardcoded bridge name in bonded compute NIC config

Remove hardcoded bridge name in bonded compute NIC config

This change removes a hardcoded value for the bond name in the NIC
config for the compute node in the bond-with-vlan NIC config
templates. When this hardcoded value of "br-bond" is used, then the
Neutron bridge mappings must be set to set to datacentre:br-bond in
order for VLAN mode networking to recognize the bridge. By using the
input value for bridge_name we will ensure that the controller and
compute nodes have the same bridge name (defaults to "br-ex"), and
that the defaults will work with VLAN mode.

Change-Id: I28654ab93e3c10a8597c8b877f3f2f6b3eca887c