Fix KeyError if neutron security group is not TCP/UDP/ICMP and no ports

Previously, if a neutron security group rule was created that was not
TCP/UDP/ICMP and did not contain a port_range_min/max retrieving it from
nova-api would result in a KeyError in nova-api. This patch resolves
this issue.

Change-Id: I6284a7a8690aec9509b63f7cbd18812e09ef3fdd
Closes-bug: #1294346
Merge "Fix KeyError if neutron security group is not TCP/UDP/ICMP and no ports"