Passed tokens may now be promises.

Tokens passed to token-requiring API methods may now also be promises,
permitting promise-based request chaining across API's. For example:

keystone
  .issueToken()
  .then((token) => glance.imageList(token));

...or:

const tokenPromise = keystone.issueToken();

Promise.all([
  glance.imageList(tokenPromise),
  neutron.networkList(tokenPromise),
  nova.flavorList(tokenPromise)
]).then(([images, networks, flavors]) => {
  return nova.instanceCreate( ... );
});

These updates have been wrapped into a private method, which can
be used for other API's as well. revokeToken is the noted exception,
as it may have to resolve TWO tokens (auth and subject).

Change-Id: I24e0a1e979d2aaedc6a25e378bd9d99f51ece595

src/keystone.js

@@ -56,6 +56,30 @@ export default class Keystone {
     return pointer;
   }
 
+  /**
+   * This method builds common components of a keystone request. It converts any passed token
+   * into a promise, resolves the base URL, and then passes the results as an .all() promise,
+   * which may be destructured in a followup request.
+   *
+   * @param {Promise|String} token A promise, or string, representing a token.
+   * @returns {Promise} A promise which resolves with [url, token].
+   * @private
+   */
+  _requestComponents (token = null) {
+    // Make sure the token is a promise.
+    let headerPromise = Promise
+      .resolve(token)
+      .then((token) => {
+        if (token) {
+          return {
+            'X-Auth-Token': token
+          };
+        }
+        return {};
+      });
+    return Promise.all([this.serviceEndpoint(), headerPromise]);
+  }
+
   /**
    * Retrieve all the API versions available.
    *
@@ -186,13 +210,15 @@ export default class Keystone {
    * @returns {Promise.<T>} A promise which will resolve if the token has been successfully revoked.
    */
   tokenRevoke (token, adminToken = null) {
-    let headers = {
-      'X-Subject-Token': token,
-      'X-Auth-Token': adminToken || token
-    };
-
-    return this.serviceEndpoint()
-      .then((url) => this.http.httpRequest('DELETE', `${url}auth/tokens`, headers));
+    return Promise
+      .all([this.serviceEndpoint(), token, adminToken])
+      .then(([url, token, adminToken]) => {
+        return [url, {
+          'X-Subject-Token': token,
+          'X-Auth-Token': adminToken || token
+        }];
+      })
+      .then(([url, headers]) => this.http.httpRequest('DELETE', `${url}auth/tokens`, headers));
   }
 
   /**
@@ -202,14 +228,9 @@ export default class Keystone {
    * @returns {Promise.<T>} A promise which will resolve with the service catalog.
    */
   catalogList (token = null) {
-    const headers = {};
-    if (token) {
-      headers['X-Auth-Token'] = token;
-    }
-
     return this
-      .serviceEndpoint()
-      .then((url) => this.http.httpRequest('GET', `${url}auth/catalog`, headers))
+      ._requestComponents(token)
+      .then(([url, headers]) => this.http.httpRequest('GET', `${url}auth/catalog`, headers))
       .then((response) => response.json())
       .then((body) => body.catalog);
   }