Delete control_exchange flag

control_exchange is duplicated in init.pp and ceilometer.pp which could
create duplicate declaration when declaring cinder and
cinder::ceilometer on same node.

Closes-bug #1266259
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>

Change-Id: Ic1c5c880c421f43d2a125b2b5b58630fc55bc9c8