Implement update of AWS::EC2::SecurityGroup rules

Such functionality is supported by AWS [1], is present in
OS::Neutron::SecurityGroup but was missing from AWS::EC2::SecurityGroup.
Updates for both Neutron and Nova-Network security groups are
implemented.
Updates are performed on per-rule basis with minimal interruption.
The implementation splits the code in two helper classes implementing
Nova and Neutron API orchestraion.

Also, security groups APIs mocks are brought closer to reality.

[1] http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-security-group.html

Change-Id: I86a04612567bd6080d1b825bc58acc9a08f0c2a4
Implements: blueprint handle-update-for-security-groups
Merge "Implement update of AWS::EC2::SecurityGroup rules"