Fix the default rpc policy value

Before, each time a service that use ceilometer.publisher.rpc start this
annoying message appear because the default value is not the correct.

WARNING ceilometer.publisher.rpc [-] Publishing policy is unknown (wait) force to default
WARNING ceilometer.publisher.rpc [-] Publishing policy is unknown (wait) force to default

This patch set the correct default (to default inteads of wait), and check in tests
that the expected logger method is called.

Fixes bug #1245965

Change-Id: I41b9461359c7b0b17eb8e9dad1772bafdc3554fc
(cherry picked from commit 30ecd2f76633b8854401c6254210aaa5a7920be0)
Merge "Fix the default rpc policy value" into stable/havana