Set correct columns' length

In migration 569e98a8132b_metering incorrect length is set for
description column (255 instead of 1024) and in migration
39cf3f799352_fwaas_havana_2_model for firewall_rules table
incorrect length is set  for protocol column (24 instead of 40).

partially implement bp: db-sync-models-with-migrations

Change-Id: I0b2cb00c3bd2cd2ac7e002c861095129e5b5aa96
Remove "reuse_existing" from setup method in dhcp.py

This flag is never used, it's always set to True by
DhcpLocalProcess.enable()

Change-Id: Ic30e0f2c97679d5919cc4e4afeb38666a6d41392
Closes-bug: #1305083
Merge "Set correct columns' length"
Merge "Remove "reuse_existing" from setup method in dhcp.py"