Add an API test for docker build -f Dockerfile

I noticed that while we have tests to make sure that people don't
specify a Dockerfile (via -f) that's outside of the build context
when using the docker cli, we don't check on the server side to make
sure that API users have the same check done. This would be a security
risk.

While in there I had to add a new util func for the tests to allow us to
send content to the server that isn't json encoded - in this case a tarball

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

integration-cli/docker_utils.go

@@ -274,6 +274,15 @@ func daemonHost() string {
 }
 
 func sockRequest(method, endpoint string, data interface{}) ([]byte, error) {
+	jsonData := bytes.NewBuffer(nil)
+	if err := json.NewEncoder(jsonData).Encode(data); err != nil {
+		return nil, err
+	}
+
+	return sockRequestRaw(method, endpoint, jsonData, "application/json")
+}
+
+func sockRequestRaw(method, endpoint string, data io.Reader, ct string) ([]byte, error) {
 	daemon := daemonHost()
 	daemonUrl, err := url.Parse(daemon)
 	if err != nil {
@@ -296,17 +305,16 @@ func sockRequest(method, endpoint string, data interface{}) ([]byte, error) {
 	client := httputil.NewClientConn(c, nil)
 	defer client.Close()
 
-	jsonData := bytes.NewBuffer(nil)
-	if err := json.NewEncoder(jsonData).Encode(data); err != nil {
-		return nil, err
-	}
-
-	req, err := http.NewRequest(method, endpoint, jsonData)
-	req.Header.Set("Content-Type", "application/json")
+	req, err := http.NewRequest(method, endpoint, data)
 	if err != nil {
 		return nil, fmt.Errorf("could not create new request: %v", err)
 	}
 
+	if ct == "" {
+		ct = "application/json"
+	}
+	req.Header.Set("Content-Type", ct)
+
 	resp, err := client.Do(req)
 	if err != nil {
 		return nil, fmt.Errorf("could not perform request: %v", err)