Disk utilisation plugin.

Returns metrics for all devices listed by iostat that do not start with
'dm-'. The metric is the %util over a period of 5 seconds from when the
check is run.
Update all scripts to have main function
Create pex files.
Command timer plugin.
Update maas_common and nova_service_check to v2

In maas_common:
The client now uses v2
get_endpoint_url_for_service defaults to internalURL

In nova_service_check:
Remove need to supply IP address, it will now use the internalURL
automatically.
Update to use version 1.4.13 of memcached
Enable use of nova v2 api.
Update disk_utilisation with main function.