Assert error in body of function inspectField*

1. Replace raw `docker inspect -f xxx` with `inspectField`, to make code
cleaner and more consistent
2. assert the error in function `inspectField*` so we don't need to
assert the return value of it every time, this will make inspect easier.

Signed-off-by: Zhang Wei <zhangwei555@huawei.com>
Upstream-commit: 62a856e9129c9d5cf7db9ea6322c9073d68e3ea4
Component: engine

components/engine/integration-cli/docker_cli_save_load_unix_test.go

@@ -6,6 +6,7 @@ import (
 	"io/ioutil"
 	"os"
 	"os/exec"
+	"strings"
 
 	"github.com/docker/docker/pkg/integration/checker"
 	"github.com/go-check/check"
@@ -19,6 +20,7 @@ func (s *DockerSuite) TestSaveAndLoadRepoStdout(c *check.C) {
 
 	repoName := "foobar-save-load-test"
 	before, _ := dockerCmd(c, "commit", name, repoName)
+	before = strings.TrimRight(before, "\n")
 
 	tmpFile, err := ioutil.TempFile("", "foobar-save-load-test.tar")
 	c.Assert(err, check.IsNil)
@@ -41,9 +43,10 @@ func (s *DockerSuite) TestSaveAndLoadRepoStdout(c *check.C) {
 	out, _, err := runCommandWithOutput(loadCmd)
 	c.Assert(err, check.IsNil, check.Commentf(out))
 
-	after, _ := dockerCmd(c, "inspect", "-f", "{{.Id}}", repoName)
+	after := inspectField(c, repoName, "Id")
+	after = strings.TrimRight(after, "\n")
 
-	c.Assert(before, check.Equals, after) //inspect is not the same after a save / load
+	c.Assert(after, check.Equals, before) //inspect is not the same after a save / load
 
 	deleteImages(repoName)