health: Dumping results in sub-directory

When VMs are reporting results to the server, let's save the resulting hw.py in a
HEALTH_DIR/dahc/ subdirectory.

As some VMs are reporting the same serial number, let's always pad the ethernet address.

A typical output looks like:
root@pod-server:/var/lib/edeploy/health/dahc/6/2014_06_30-13h50# ls -al
-rw-r--r-- 1 root root 2553 Jun 30 13:50 OpenStackCompute-RedHat-44454c4c4b0010398050b9c04f573032-fa-16-3e-bf-a1-07.hw
-rw-r--r-- 1 root root 2555 Jun 30 13:50 OpenStackCompute-RedHat-44454c4c4b0010398056b9c04f573032-fa-16-3e-26-c8-1c.hw
-rw-r--r-- 1 root root 2555 Jun 30 13:50 OpenStackCompute-RedHat-44454c4c4b0010398056b9c04f573032-fa-16-3e-63-6f-24.hw
-rw-r--r-- 1 root root 2555 Jun 30 13:50 OpenStackCompute-RedHat-44454c4c4b0010398058c2c04f573032-fa-16-3e-0f-e7-06.hw
-rw-r--r-- 1 root root 2555 Jun 30 13:50 OpenStackCompute-RedHat-44454c4c4b0010398058c2c04f573032-fa-16-3e-34-d3-9d.hw
-rw-r--r-- 1 root root 2555 Jun 30 13:50 OpenStackCompute-RedHat-44454c4c4b0010398058c2c04f573032-fa-16-3e-89-9a-9c.hw
-rw-r--r-- 1 root root 2555 Jun 30 13:50 OpenStackCompute-RedHat-44454c4c4b0010398058c2c04f573032-fa-16-3e-c0-aa-a6.hw