Fix ceilomter-api bind host config settings

With the enablement of haproxy, services need to bind to the correct
address else conflicts will occur between services and haproxy.  Config
templates were updated in I2aca62a8da61221d67f7a99bc33a6e4ebfa53acd, but
ceilometer.conf requires this setting to be configured in the [api] section
using the 'host' flag.

Change-Id: I664c10ffca7f3bc401adcbf502963da3fcbe6038
Closes-bug: #1337707