Add container state metrics to docker plugin (#1791)

* Add container state metrics to docker plugin.

* Update changelog.

plugins/inputs/docker/README.md

@@ -103,6 +103,9 @@ based on the availability of per-cpu stats on your system.
     - n_used_file_descriptors
     - n_cpus
     - n_containers
+    - n_containers_running
+    - n_containers_stopped
+    - n_containers_paused
     - n_images
     - n_goroutines
     - n_listener_events
@@ -153,6 +156,9 @@ based on the availability of per-cpu stats on your system.
 > docker n_cpus=8i 1456926671065383978
 > docker n_used_file_descriptors=15i 1456926671065383978
 > docker n_containers=7i 1456926671065383978
+> docker n_containers_running=7i 1456926671065383978
+> docker n_containers_stopped=3i 1456926671065383978
+> docker n_containers_paused=0i 1456926671065383978
 > docker n_images=152i 1456926671065383978
 > docker n_goroutines=36i 1456926671065383978
 > docker n_listener_events=0i 1456926671065383978

plugins/inputs/docker/docker.go

@@ -154,6 +154,9 @@ func (d *Docker) gatherInfo(acc telegraf.Accumulator) error {
 		"n_cpus":                  info.NCPU,
 		"n_used_file_descriptors": info.NFd,
 		"n_containers":            info.Containers,
+		"n_containers_running":    info.ContainersRunning,
+		"n_containers_stopped":    info.ContainersStopped,
+		"n_containers_paused":     info.ContainersPaused,
 		"n_images":                info.Images,
 		"n_goroutines":            info.NGoroutines,
 		"n_listener_events":       info.NEventsListener,

plugins/inputs/docker/docker_test.go

@@ -256,6 +256,9 @@ type FakeDockerClient struct {
 func (d FakeDockerClient) Info(ctx context.Context) (types.Info, error) {
 	env := types.Info{
 		Containers:         108,
+		ContainersRunning:  98,
+		ContainersStopped:  6,
+		ContainersPaused:   3,
 		OomKillDisable:     false,
 		SystemTime:         "2016-02-24T00:55:09.15073105-05:00",
 		NEventsListener:    0,
@@ -397,6 +400,9 @@ func TestDockerGatherInfo(t *testing.T) {
 			"n_cpus":                  int(4),
 			"n_used_file_descriptors": int(19),
 			"n_containers":            int(108),
+			"n_containers_running":    int(98),
+			"n_containers_stopped":    int(6),
+			"n_containers_paused":     int(3),
 			"n_images":                int(199),
 			"n_goroutines":            int(39),
 		},