Move Go() promise-like func from utils to pkg/promise

This is the first of two steps to break the archive package's dependence
on utils so that archive may be moved into pkg.  Also, the `Go()`
function is small, concise, and not specific to the docker internals, so
it is a good candidate for pkg.

Signed-off-by: Rafe Colton <rafael.colton@gmail.com>
Upstream-commit: b845a62149d5f4990462ac6c9167c5cfaa0e66cb
Component: engine

components/engine/daemon/attach.go

@@ -10,6 +10,7 @@ import (
 	"github.com/docker/docker/pkg/ioutils"
 	"github.com/docker/docker/pkg/jsonlog"
 	"github.com/docker/docker/pkg/log"
+	"github.com/docker/docker/pkg/promise"
 	"github.com/docker/docker/utils"
 )
 
@@ -246,7 +247,7 @@ func (daemon *Daemon) Attach(streamConfig *StreamConfig, openStdin, stdinOnce, t
 		}()
 	}
 
-	return utils.Go(func() error {
+	return promise.Go(func() error {
 		defer func() {
 			if cStdout != nil {
 				cStdout.Close()

components/engine/daemon/container.go

@@ -27,6 +27,7 @@ import (
 	"github.com/docker/docker/pkg/log"
 	"github.com/docker/docker/pkg/networkfs/etchosts"
 	"github.com/docker/docker/pkg/networkfs/resolvconf"
+	"github.com/docker/docker/pkg/promise"
 	"github.com/docker/docker/pkg/symlink"
 	"github.com/docker/docker/runconfig"
 	"github.com/docker/docker/utils"
@@ -1117,7 +1118,7 @@ func (container *Container) waitForStart() error {
 	// process or until the process is running in the container
 	select {
 	case <-container.monitor.startSignal:
-	case err := <-utils.Go(container.monitor.Start):
+	case err := <-promise.Go(container.monitor.Start):
 		return err
 	}
 

components/engine/daemon/exec.go

@@ -15,6 +15,7 @@ import (
 	"github.com/docker/docker/pkg/broadcastwriter"
 	"github.com/docker/docker/pkg/ioutils"
 	"github.com/docker/docker/pkg/log"
+	"github.com/docker/docker/pkg/promise"
 	"github.com/docker/docker/runconfig"
 	"github.com/docker/docker/utils"
 )
@@ -254,7 +255,7 @@ func (container *Container) Exec(execConfig *execConfig) error {
 
 	// We use a callback here instead of a goroutine and an chan for
 	// syncronization purposes
-	cErr := utils.Go(func() error { return container.monitorExec(execConfig, callback) })
+	cErr := promise.Go(func() error { return container.monitorExec(execConfig, callback) })
 
 	// Exec should not return until the process is actually running
 	select {