Allow hostnames to be used as ip_address

Previously introduced change for monasca-persister
had enforced the IPAddress as the only type one can
configure influxdb.ip_address property with.

Following change makes it possible to use also hostname.
Using IPAdress is still possible.

Change-Id: Ib0d7f19b3ac2dcb7c84923872d94f180cda58b2b
(cherry picked from commit 66fe6f98c079490d2d5de4c161da1d8b3801cda4)

monasca_persister/conf/influxdb.py

@@ -20,8 +20,9 @@ influxdb_opts = [
     cfg.StrOpt('database_name',
                help='database name where metrics are stored',
                default='mon'),
-    cfg.IPOpt('ip_address',
-              help='ip address to influxdb'),
+    cfg.HostAddressOpt('ip_address',
+                       help='Valid IP address or hostname '
+                            'to InfluxDB instance'),
     cfg.PortOpt('port',
                 help='port to influxdb',
                 default=8086),