Updated openstack/openstack
Project: openstack/ceilometer  e63ee553178cec0d09ebf8a327e36b8c0bd15227
null
Fix the return of statistic with getting no sample

In mysql scenario, when getting statistics with no sample
(this can be presented with invalid value of sample filters), ceilometer
will raise an error about NoneType.
Like other API of ceilometer, it should return an empty list.

Change-Id: I07cbc3f03f7a5e6751e6851f14ed1cdc16ee4a4c
Closes-bug: #1292322