@Upayavira:
I have an update regarding this issue.
According to https://wiki.strongswan.org/issues/183 we need the kernel to be compiled with CONFIG_INET_XFRM_MODE_TRANSPORT set. If you look at the boot2docker kernel config(/proc/config.gz), you will notice that this flag is not set and commented out. Hence strongswan is not able to push the CHILD_SA even though the tunnel is established.
In short, cross host communication will not work using boot2docker image.
So to get rancher to work properly on your laptop, try using some other OS. I have tried installing Ubuntu (14.04.4 LTS) and it worked totally fine. For Ubuntu, the kernel config info is available at a different place (/boot/config-*).
So please create different Virtualbox VMs using a different OS, start rancher server, agents and test it out. I am sure you will see the cross host communication working.
Let me know how it goes.