Use FakeCeilometerClient instead of mocks

FakeCeilometerClient can be used instead of mocking ceilometer
client from osclients completely. This patch implements
FakeCeilometerClient and modifies tests for ceilometer components.

blueprint: benchmark-scenarios-for-celiometer
Change-Id: I2fcdb2bc3e1a70a1ff2c05a8939ca1de171bd4c0