Fix description of service in keystone catalog

It was mentioning Collector instead of Telemetry.
Remove trailing slashes from endpoints

See https://bugs.launchpad.net/python-ceilometerclient/+bug/1262498
Make interval for disk & network configurable

The general interval for meters might not be what is wanted for these
sources.
Merge pull request #137 from vuntz/more-intervals

Make interval for disk & network configurable
Merge pull request #135 from vuntz/endpoint-fixes

Small fixes for the catalog registration