Support Neutron security groups in scenario testing

The methods
NetworkScenarioTest._create_security_group()
and
NetworkScenarioTest.create_loginable_secgroup_rule()
use the nova client by default.

Added helper functions "*_neutron" that use the neutron (network)
client.
Moved old implementation into "*_nova" for old usage.

Adds methods to scenario/manager to allow for generic creation of
neutron secgroup and rules as existing methods only create a secgroup
with login rules (incoming ping and ssh).

Change-Id: I6de4bf9f7deed215cf61c87c3ae3f4240982523e
Merge "Support Neutron security groups in scenario testing"