Ceilometer can conditionally delegate and redirect all alarm related
activity to Aodh. This can now be auto-enabled through this variable
combined with the related change in the os_ceilometer role. A
deployers can force-disable this integration by overriding the var.
Related Change: I4a3f6b69b6b19118248c383c1d58c99e1a7f8262
Change-Id: I440b4c8127eff2dc517d7ff8e277c6d7a5f106ce