Implement timeouts for all exec command runners

First is to write an internal CombinedOutput and Run function with a
timeout.

Second, the following instances of command runners need to have timeouts:

    plugins/inputs/ping/ping.go
    125:	out, err := c.CombinedOutput()

    plugins/inputs/exec/exec.go
    91:	if err := cmd.Run(); err != nil {

    plugins/inputs/ipmi_sensor/command.go
    31:	err := cmd.Run()

    plugins/inputs/sysstat/sysstat.go
    194:	out, err := cmd.CombinedOutput()

    plugins/inputs/leofs/leofs.go
    185:	defer cmd.Wait()

    plugins/inputs/sysstat/sysstat.go
    282:	if err := cmd.Wait(); err != nil {

closes #1067

plugins/inputs/ping/ping.go

@@ -9,15 +9,17 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"time"
 
 	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/internal"
 	"github.com/influxdata/telegraf/plugins/inputs"
 )
 
 // HostPinger is a function that runs the "ping" function using a list of
 // passed arguments. This can be easily switched with a mocked ping function
 // for unit test purposes (see ping_test.go)
-type HostPinger func(args ...string) (string, error)
+type HostPinger func(timeout float64, args ...string) (string, error)
 
 type Ping struct {
 	// Interval at which to ping (ping -i <INTERVAL>)
@@ -74,7 +76,7 @@ func (p *Ping) Gather(acc telegraf.Accumulator) error {
 		go func(u string) {
 			defer wg.Done()
 			args := p.args(u)
-			out, err := p.pingHost(args...)
+			out, err := p.pingHost(p.Timeout, args...)
 			if err != nil {
 				// Combine go err + stderr output
 				errorChannel <- errors.New(
@@ -116,13 +118,14 @@ func (p *Ping) Gather(acc telegraf.Accumulator) error {
 	return errors.New(strings.Join(errorStrings, "\n"))
 }
 
-func hostPinger(args ...string) (string, error) {
+func hostPinger(timeout float64, args ...string) (string, error) {
 	bin, err := exec.LookPath("ping")
 	if err != nil {
 		return "", err
 	}
 	c := exec.Command(bin, args...)
-	out, err := c.CombinedOutput()
+	out, err := internal.CombinedOutputTimeout(c,
+		time.Second*time.Duration(timeout+1))
 	return string(out), err
 }
 

plugins/inputs/ping/ping_test.go

@@ -124,7 +124,7 @@ func TestArgs(t *testing.T) {
 		"Expected: %s Actual: %s", expected, actual)
 }
 
-func mockHostPinger(args ...string) (string, error) {
+func mockHostPinger(timeout float64, args ...string) (string, error) {
 	return linuxPingOutput, nil
 }
 
@@ -161,7 +161,7 @@ PING www.google.com (216.58.218.164) 56(84) bytes of data.
 rtt min/avg/max/mdev = 35.225/44.033/51.806/5.325 ms
 `
 
-func mockLossyHostPinger(args ...string) (string, error) {
+func mockLossyHostPinger(timeout float64, args ...string) (string, error) {
 	return lossyPingOutput, nil
 }
 
@@ -192,7 +192,7 @@ Request timeout for icmp_seq 0
 2 packets transmitted, 0 packets received, 100.0% packet loss
 `
 
-func mockErrorHostPinger(args ...string) (string, error) {
+func mockErrorHostPinger(timeout float64, args ...string) (string, error) {
 	return errorPingOutput, errors.New("No packets received")
 }
 
@@ -215,7 +215,7 @@ func TestBadPingGather(t *testing.T) {
 	acc.AssertContainsTaggedFields(t, "ping", fields, tags)
 }
 
-func mockFatalHostPinger(args ...string) (string, error) {
+func mockFatalHostPinger(timeout float64, args ...string) (string, error) {
 	return fatalPingOutput, errors.New("So very bad")
 }