Add API binding options

Ceilometer is able to bind API server to both an IP address and a port.
This patch aims to add support for both configuration flags.

Change-Id: I83164a925cf115d091cb04d14922ee7bbdd0ac63
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
(cherry picked from commit f8eea90cd9f1652ba927bfcc9bf8234af8983c11)