Add support for Samples coming from Ceilometer

Can add or list Samples only. Samples are a sub-resource under a
Metric. Query-String filtering of samples is supported. The common
Resource type is changed to allow aliasing of resource attribute
names, required because Sample has two published and supported
resource formats within a single API version.

Change-Id: Ia1f157bffcd74dde203488917f2d5fa1df7e44aa
Merge "Add support for Samples coming from Ceilometer"