Setup rabbitmq to use keepalives (https://bugs.launchpad.net/nova/+bug/856764) & rewrote its ha-all policy

Neutron DHCP Agent now passes a MTU (1438 by default) to instances to make Neutron networks working on a physical network swhich don't allow jumboframes

Fixed neutron-vpn-agent service conflict with neutron-l3-agent service & added some mandatory sysctl parameters

Fixed various timeout values, keep-alive parameters & "backup" option for HAProxy - Galera to avoid unexpected socket closes, failed SQL transactions, etc.

- Network configuration (such as IP addresses, default gateway...) shall now be set up beforehand. It is not done by the base class anymore. We now simply use the IPs from configured interfaces.
- Reworked +Fixed some things in Neutron networking services too.

Moved nova::etwork::neutron configuration from nova/compute to nova/common since it is required to tell Nova to use Neutron secgroups.

Removed database_idle_timeout as it is not necessary anymore since 6f05de06 and updated two HAProxy IP addresses

Added/Fixed Neutron services for server/router/client. The router works well even when we only have one NIC