Change report_interval from 4 to 30, agent_down_time from 9 to 75

Defaults values changed in neutron upstream to improve performances at
large scale.
Patch in Neutron: http://git.io/U1oCmA

Change-Id: Ie79668858eaa34de3872733af06b27e926593973
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Merge "Change report_interval from 4 to 30, agent_down_time from 9 to 75"