functional: support running etcdctl from functional tests

Introduce new helpers for running etcdctl.

build-env

@@ -21,3 +21,4 @@ eval $(go env)
 export PATH="${GOROOT}/bin:${PATH}"
 export FLEETD_BIN="$(pwd)/bin/fleetd"
 export FLEETCTL_BIN="$(pwd)/bin/fleetctl"
+export ETCDCTL_BIN="/usr/bin/etcdctl"

functional/util/util.go

@@ -25,6 +25,7 @@ import (
 )
 
 var fleetctlBinPath string
+var etcdctlBinPath string
 
 func init() {
 	fleetctlBinPath = os.Getenv("FLEETCTL_BIN")
@@ -36,6 +37,15 @@ func init() {
 		os.Exit(1)
 	}
 
+	etcdctlBinPath = os.Getenv("ETCDCTL_BIN")
+	if etcdctlBinPath == "" {
+		fmt.Println("ETCDCTL_BIN environment variable must be set")
+		os.Exit(1)
+	} else if _, err := os.Stat(etcdctlBinPath); err != nil {
+		fmt.Printf("%v\n", err)
+		os.Exit(1)
+	}
+
 	if os.Getenv("SSH_AUTH_SOCK") == "" {
 		fmt.Println("SSH_AUTH_SOCK environment variable must be set")
 		os.Exit(1)
@@ -76,6 +86,38 @@ func RunFleetctlWithInput(input string, args ...string) (string, string, error)
 	return stdoutBytes.String(), stderrBytes.String(), err
 }
 
+func RunEtcdctl(args ...string) (string, string, error) {
+	log.Printf("%s %s", etcdctlBinPath, strings.Join(args, " "))
+	var stdoutBytes, stderrBytes bytes.Buffer
+	cmd := exec.Command(etcdctlBinPath, args...)
+	cmd.Stdout = &stdoutBytes
+	cmd.Stderr = &stderrBytes
+	err := cmd.Run()
+	return stdoutBytes.String(), stderrBytes.String(), err
+}
+
+func RunEtcdctlWithInput(input string, args ...string) (string, string, error) {
+	log.Printf("%s %s", etcdctlBinPath, strings.Join(args, " "))
+	var stdoutBytes, stderrBytes bytes.Buffer
+	cmd := exec.Command(etcdctlBinPath, args...)
+	cmd.Stdout = &stdoutBytes
+	cmd.Stderr = &stderrBytes
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		return "", "", err
+	}
+
+	if err = cmd.Start(); err != nil {
+		return "", "", err
+	}
+
+	stdin.Write([]byte(input))
+	stdin.Close()
+	err = cmd.Wait()
+
+	return stdoutBytes.String(), stderrBytes.String(), err
+}
+
 // ActiveToSingleStates takes a map of active states (such as that returned by
 // WaitForNActiveUnits) and ensures that each unit has at most a single active
 // state. It returns a mapping of unit name to a single UnitState.