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_events_test.go

@@ -336,8 +336,7 @@ func (s *DockerSuite) TestEventsFilterContainer(c *check.C) {
 
 	for _, name := range []string{"container_1", "container_2"} {
 		dockerCmd(c, "run", "--name", name, "busybox", "true")
-		id, err := inspectField(name, "Id")
-		c.Assert(err, checker.IsNil)
+		id := inspectField(c, name, "Id")
 		nameID[name] = id
 	}