carbonara: implement an integer sampling attribute
carbonara: implement an integer sampling attribute

Currently, the sampling attribute is a Pandas object that can be either
Nano or Seconds. This is not consistent, and exposes Pandas outside of
Carbonara, which is not a good idea.

This implements a public sampling attribute which always returns a float
of the number of seconds.

Change-Id: I2cf08ee7bb0727783131728eca08888ec047a4ef

gnocchixyz/gnocchi,leandroreox/gnocchi,sileht/gnocchi,sileht/gnocchi,leandroreox/gnocchi,gnocchixyz/gnocchi