OS Ceilometer API support

OpenStack Ceilometer API's support (Skeleton & meters/samples API)

open issue I need help with -
meters and samples can get query params, problem is they cant be sent as null/empty string since ceilometer fails. example - {"filter": "", "orderby": "", "limit": ""}
need a way to avoid sending empty query params 

Fortunately, there is a utility method `Strings.isNullOrEmpty(value)` that can be used here instead.