[Build 12]:Ubuntu:SG: inconsistent traffic flow behavior with only ingress and only egress rule on diff VMs

test steps:
1. create 2 security groups "onlyEgress"(allow all egress) and "onlyIngress"(allow all ingress).
2. have 2 VNs, each having 1 VM. (say vm1-vn1 and vm1-vn2)
3. attach SG onlyEgress to vm1-vn2 and SG onlyIngress to vm1-vn1.
4. ping from vm1-vn1 to vm1-vn2 and vice versa.

expected result:
traffic vm1-vn2 ------> vm1-vn1 should be allowed
traffic vm1-vn1 ------> vm1-vn2 should be denied

but sometime traffic is ALLOWED from both sides and sometime both way traffic is DENIED.

Naveen has debugged the issue and as per his comments its because of same icmp id alloted in traffic from both side.

setup info:
env.roledefs = {
    'all': [host1,host2,host3,host4,host5],
    'cfgm': [host1,host2,host5],
    'openstack':[host2],
    'control': [host2,host1],
    'compute': [host3,host4],
    'collector': [host2,host1],
    'webui': [host1],
    'database': [host1,host2],
    'build': [host_build],
}

env.hostnames = {
    'all': ['nodeh1', 'nodeg18', 'nodeh8', 'nodec11', 'nodec12']
}