Ceph: represent pgmap states using tags (#2229)

* ceph: maps are already refs, no need to use a pointer

* ceph: pgmap_states are represented in a single metric "count", differenciated by tag

* Update CHANGELOG

CHANGELOG.md

@@ -2,6 +2,24 @@
 
 ### Release Notes
 
+- Ceph: the `ceph_pgmap_state` metric content has been modified to use a unique field `count`, with each state expressed as a `state` tag.
+
+Telegraf < 1.3:
+
+```
+# field_name             value
+active+clean             123
+active+clean+scrubbing   3
+```
+
+Telegraf >= 1.3:
+
+```
+# field_name    value       tag
+count           123         state=active+clean
+count           3           state=active+clean+scrubbing
+```
+
 - The [Riemann output plugin](./plugins/outputs/riemann) has been rewritten
 and the previous riemann plugin is _incompatible_ with the new one. The reasons
 for this are outlined in issue [#1878](https://github.com/influxdata/telegraf/issues/1878).
@@ -14,6 +32,7 @@ It is highly recommended that all users migrate to the new riemann output plugin
 - [#2204](https://github.com/influxdata/telegraf/pull/2204): Extend http_response to support searching for a substring in response. Return 1 if found, else 0.
 - [#2137](https://github.com/influxdata/telegraf/pull/2137): Added userstats to mysql input plugin.
 - [#2179](https://github.com/influxdata/telegraf/pull/2179): Added more InnoDB metric to MySQL plugin.
+- [#2229](https://github.com/influxdata/telegraf/pull/2229): `ceph_pgmap_state` metric now uses a single field `count`, with PG state published as `state` tag. 
 - [#2251](https://github.com/influxdata/telegraf/pull/2251): InfluxDB output: use own client for improved through-put and less allocations.
 - [#2330](https://github.com/influxdata/telegraf/pull/2330): Keep -config-directory when running as Windows service.
 - [#1900](https://github.com/influxdata/telegraf/pull/1900): Riemann plugin rewrite.