pass tenant- as prefix to tenant name.

this is how we're now doing it for other plugins.
use tenant- as prefix to tenant name.
new go at collecting volumes and snapshots data.

need to ask for limits to get the quotas, and list all the volumes with
all_tenants=1 and then go throught them to get the tenant specific usage
values ( limits is missing the usage metrics in havana ).

Fixes #7.
use collectd.info for logdebug.

this way we can have plugin specific debug configs without having to
enable the global collectd debugging.
fixes neutron related usage and quotas.

adds quota info directly from neutron.

counts the number of used floating ips per tenant, by listing the full
list of used floating ips (reason is the nova limits data in havana
gives back bogus info).

Fixes #8.