Fixes security rules in Midonet plugin

Fixes several issues with the rule chains in Midonet plugins, including
adding a rule to drop egress traffic by default, adding security group
support to a port's egress chain, and correctly adding/deleting jump
rules from port chains when changing a port's security groups. Also
fixes several pep8 issues.

Change-Id: Ib80bd22135b220b0e8113556ac7a2b2d9261c954
Closes-Bug: #1231790
Replace Midonet port groups with IP address groups

Replacing port groups with IP address groups. With Neutron security
groups implemented as Midonet port groups, we were unable to support
security rules with security group as a criterion because we didn't
know the destination port at the time of egress to the network. This
change implements neutron security groups as Midonet IP address
groups. This allows us to perform the security group check because the
destination IP address is known at all times.

Change-Id: Ia60ba8edf94406520b36ef4e465574b6e5fb3c0d
Closes-Bug: #1244025