Remove panic in nat package on invalid hostport

Closes #14621

This one grew to be much more than I expected so here's the story... :-)
- when a bad port string (e.g. xxx80) is passed into container.create()
  via the API it wasn't being checked until we tried to start the container.
- While starting the container we trid to parse 'xxx80' in nat.Int()
  and would panic on the strconv.ParseUint().  We should (almost) never panic.
- In trying to remove the panic I decided to make it so that we, instead,
  checked the string during the NewPort() constructor.  This means that
  I had to change all casts from 'string' to 'Port' to use NewPort() instead.
  Which is a good thing anyway, people shouldn't assume they know the
  internal format of types like that, in general.
- This meant I had to go and add error checks on all calls to NewPort().
  To avoid changing the testcases too much I create newPortNoError() **JUST**
  for the testcase uses where we know the port string is ok.
- After all of that I then went back and added a check during container.create()
  to check the port string so we'll report the error as soon as we get the
  data.
- If, somehow, the bad string does get into the metadata we will generate
  an error during container.start() but I can't test for that because
  the container.create() catches it now.  But I did add a testcase for that.

Signed-off-by: Doug Davis <dug@us.ibm.com>

integration-cli/docker_api_containers_test.go

@@ -872,6 +872,32 @@ func (s *DockerSuite) TestContainerApiCommitWithLabelInConfig(c *check.C) {
 	dockerCmd(c, "run", img.Id, "ls", "/test")
 }
 
+func (s *DockerSuite) TestContainerApiBadPort(c *check.C) {
+	config := map[string]interface{}{
+		"Image": "busybox",
+		"Cmd":   []string{"/bin/sh", "-c", "echo test"},
+		"PortBindings": map[string]interface{}{
+			"8080/tcp": []map[string]interface{}{
+				{
+					"HostIp":   "",
+					"HostPort": "aa80",
+				},
+			},
+		},
+	}
+
+	jsonData := bytes.NewBuffer(nil)
+	json.NewEncoder(jsonData).Encode(config)
+
+	status, b, err := sockRequest("POST", "/containers/create", config)
+	c.Assert(err, check.IsNil)
+	c.Assert(status, check.Equals, http.StatusInternalServerError)
+
+	if strings.TrimSpace(string(b)) != `Invalid port specification: "aa80"` {
+		c.Fatalf("Incorrect error msg: %s", string(b))
+	}
+}
+
 func (s *DockerSuite) TestContainerApiCreate(c *check.C) {
 	config := map[string]interface{}{
 		"Image": "busybox",