Product license verification in Console (#518)

Operator UI - Provide and store License key
- New License section in Operator UI will allow user to provide the
  license key via input form
- New License section in Operator UI will allow the user to fetch the
  license key using subnet credentials
-  Console backend has to verify provided license is valid -
   https://godoc.org/github.com/minio/minio/pkg/licverifier#example-package
-  Console backend has to store the license key in k8s secrets

Operator UI - Set license to tenant during provisioning
- Check if license key exists in k8s secret during tenant creation
- If License is present attach the license-key jwt to the new console
tenant via an environment variable

Operator UI - Set license for an existing tenant
- Tenant view will display information about the current status of the
  Tenant License
- If Tenant doesn't have a License then Operator-UI will allow to attach
new license by clicking the Add License button
- Console backend will extract the license from the k8s secret and save
the license-key jwt in the tenant console environment variable and
redeploy

cluster/http_client.go

@@ -17,6 +17,7 @@
 package cluster
 
 import (
+	"io"
 	"net/http"
 )
 
@@ -25,6 +26,8 @@ import (
 // that are used within this project.
 type HTTPClientI interface {
 	Get(url string) (resp *http.Response, err error)
+	Post(url, contentType string, body io.Reader) (resp *http.Response, err error)
+	Do(req *http.Request) (*http.Response, error)
 }
 
 // HTTPClient Interface implementation
@@ -38,3 +41,13 @@ type HTTPClient struct {
 func (c *HTTPClient) Get(url string) (resp *http.Response, err error) {
 	return c.Client.Get(url)
 }
+
+// Post implements http.Client.Post()
+func (c *HTTPClient) Post(url, contentType string, body io.Reader) (resp *http.Response, err error) {
+	return c.Client.Post(url, contentType, body)
+}
+
+// Do implements http.Client.Do()
+func (c *HTTPClient) Do(req *http.Request) (*http.Response, error) {
+	return c.Client.Do(req)
+}