implement VlanManager support for nova-network OCF script

- factor out firewall and dnsmasq related actions, because they are same
  for both nova-network network managers (FlatDHCPManager and VlanManager)
- flush IP addresses assigned by nova-network service to network bridges
  in case of VlanManager
- remove warning about unsupported VlanManager
- be more strict about dnsmasq processes: first try to stop them with
  TERM signal several times, then if they are still exist try to send
  them KILL signal
- switch /bin/sh to /bin/bash, because on Ubuntu /bin/sh does not
  support constructions like this $((alive++))

Change-Id: I816336d83dc84cdfe0aa68ef3f8d742e4aa6e030
Closes-bug: #1392719
Merge "implement VlanManager support for nova-network OCF script"