mark deprecated ceilometer items

this patch:
- adds note that ceilometer-polling is the recommended service to
  use when polling compute, central, or ipmi data.
- marks db2nosql driver as deprecated as it is not longer developed
  by ibm.
- mark RPC publisher as deprecated for notifier publisher.

Change-Id: I34838dd17c681cae0fa360f8648434f3d777323f

doc/admin-guide-cloud/source/telemetry-data-retrieval.rst

@@ -416,7 +416,8 @@ rpc
     It can be specified in the form of
     ``rpc://?option1=value1&option2=value2``. It emits metering data
     over lossy AMQP. This method is synchronous and may experience
-    performance issues.
+    performance issues. This publisher is deprecated in Liberty in favour of
+    the notifier publisher.
 
 udp
     It can be specified in the form of ``udp://<host>:<port>/``. It emits
@@ -493,5 +494,5 @@ specified. A sample ``publishers`` section in the
 
     publishers:
         - udp://10.0.0.2:1234
-        - rpc://?per_meter_topic=1
+        - rpc://?per_meter_topic=1 (deprecated in Liberty)
         - notifier://?policy=drop&max_queue_length=512

doc/admin-guide-cloud/source/telemetry-system-architecture.rst

@@ -16,7 +16,8 @@ ceilometer-api
 
 ceilometer-polling
     Polls for different kinds of meter data by using the polling
-    plug-ins (pollsters) registered in different namespaces.
+    plug-ins (pollsters) registered in different namespaces. It provides a
+    single polling interface across different namespaces.
 
 ceilometer-agent-central
     Polls the public RESTful APIs of other OpenStack services such as
@@ -53,6 +54,8 @@ ceilometer-alarm-notifier
     .. note::
 
        The ``ceilometer-polling`` service is available since the Kilo release.
+       It is intended to replace ceilometer-agent-central,
+       ceilometer-agent-compute, and ceilometer-agent-ipmi.
 
 Besides the ``ceilometer-agent-compute`` and the ``ceilometer-agent-ipmi``
 services, all the other services are placed on one or more controller
@@ -89,7 +92,12 @@ The list of supported database back ends:
 
 -  `HBase <http://hbase.apache.org/>`__
 
--  `DB2 <http://www-01.ibm.com/software/data/db2/>`__
+-  `DB2(deprecated) <http://www-01.ibm.com/software/data/db2/>`__
+
+.. note::
+
+   DB2 nosql support is deprecated as of Liberty and will be removed in Mitaka
+   as the product is no longer in development.
 
 |