[baremetal] Re-assign mgmt network to proxy nodes

[baremetal] Re-assign mgmt network to proxy nodes

- extend arch-specific list of predefined VM iface names (2 -> 3);
- add extra vnet iface for prx0* VCP VMs, connected to br-ctl (mgmt);
- add mgmt address to pod_config.yml template (and sample);
- add mgmt address to reclass.storage prx nodes;

JIRA: FUEL-302

Change-Id: I17ce65eade7f69219fc27264363364e3c47d8f3f
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
(cherry picked from commit 35041f05e790f8c13782eb4956b991a97fdec853)