Ceph Cluster Performance Input Plugin

The existing ceph input plugin only has access to the local admin daemon socket
on the local host, and as such has access to a limited subset of data.  This
extends the plugin to use CLI commands to get access to the full spread of Ceph
data.  This patch collects global OSD map and IO statistics, PG state and per pool
IO and utilization statistics.

closes #1513

etc/telegraf.conf

@@ -511,6 +511,10 @@
 
 # # Collects performance metrics from the MON and OSD nodes in a Ceph storage cluster.
 # [[inputs.ceph]]
+#   ## This is the recommended interval to poll.  Too frequent and you will lose
+#   ## data points due to timeouts during rebalancing and recovery
+#   interval = '1m'
+#
 #   ## All configuration values are optional, defaults are shown below
 #
 #   ## location of ceph binary
@@ -525,6 +529,26 @@
 #
 #   ## suffix used to identify socket files
 #   socket_suffix = "asok"
+#
+#   ## Ceph user to authenticate as, ceph will search for the corresponding keyring
+#   ## e.g. client.admin.keyring in /etc/ceph, or the explicit path defined in the
+#   ## client section of ceph.conf for example:
+#   ##
+#   ##     [client.telegraf]
+#   ##         keyring = /etc/ceph/client.telegraf.keyring
+#   ##
+#   ## Consult the ceph documentation for more detail on keyring generation.
+#   ceph_user = "client.admin"
+#
+#   ## Ceph configuration to use to locate the cluster
+#   ceph_config = "/etc/ceph/ceph.conf"
+#
+#   ## Whether to gather statistics via the admin socket
+#   gather_admin_socket_stats = true
+#
+#   ## Whether to gather statistics via ceph commands, requires ceph_user and ceph_config
+#   ## to be specified
+#   gather_cluster_stats = true
 
 
 # # Read specific statistics per cgroup