adds a helper class, converts glance to use it.

this commit adds a common helper class, which should be used by all
plugins. also converts the glance plugin to use it.
refactored to have a common base class for all plugins.

this commit introduces the base module, and the Base class inside of it.
this is the super class of all the plugins, and provides common methods
to parse metrics, read/config the plugin, retrieve keystone objects,
etc.

keystone, glance and nova have been refactored to use it.

other changes:
- nova plugin now publishes limits and quotas info
removed ceph plugin files.

they'll be put in a separate pkg.
dropped swift_stats, not sure what it's doing.
finalized cinder and neutron plugins.

plus some minor changes in glance and nova.
updated debian pkg files for new release.
updated readme instructions for ppa pkg upload.
fixed issue with verbose logging.
updated for version 0.3.
fixed typo in changelog.
one more typo in changelog fixed.
minor update in readme / deb build.
pass the tenant id instead of the name to nova limits.
added network related quotas.

namely routers, networks, subnets, floatingips, ports.

some of them are also exposed in the compute limits call, but not all so
we need to add these too.
moved plugins to /usr/lib/collectd/plugins/openstack.

and new release 0.3-2 for debian to reflect this.
up version to 0.4
add missing __init__.py files.

Fixes #2 by adding the missing file to turn the plugins dir into a
python package that can be referenced.
fixes neutron plugin quotas, drops useless packaging files.

fixes bug #3, which prevents the neutron plugin from failing when a
tenant has no quotas defined.
dropped unused debian pkging file.
protected against missing tenant_id in cinder/neutron.

adds a wrapper for snapshots/volumes in cinder and networks in neutron
for the cases where their associated tenant_id does not exist any more.
this should never happen, but was seen in a production setup.

Fixes #4.