[openstack|storage] Added support to impersonate other accounts

The patch would allow to impersonate other accounts if you have
an admin role:

     require 'fog'
     require 'pp'

     auth_url = 'https://identity.test.lan/v2.0/tokens'
     user = 'admin@test.lan'
     password = 'secret'

     id = Fog::Identity.new :provider => 'OpenStack',
                            :openstack_auth_url => auth_url,
                            :openstack_username => user,
                            :openstack_api_key  => password

     st = Fog::Storage.new :provider => 'OpenStack',
                           :openstack_auth_url => auth_url,
                           :openstack_username => user,
                           :openstack_api_key  => password

     id.tenants.each do |t|
       puts "Changing account to #{t.name}"
       st.change_account "AUTH_#{t.id}"
       # list account containers
       pp st.directories
       # We could also head the account and get usage information
       pp st.request :method => 'HEAD'
     end

lib/fog/openstack/storage.rb

@@ -84,6 +84,52 @@ module Fog
           @connection.reset
         end
 
+        # Change the current account while re-using the auth token.
+        #
+        # This is usefull when you have an admin role and you're able
+        # to HEAD other user accounts, set quotas, list files, etc.
+        #
+        # For example:
+        #
+        #     # List current user account details
+        #     service = Fog::Storage[:openstack]
+        #     service.request :method => 'HEAD'
+        #     
+        # Would return something like:
+        #
+        #     Account:                      AUTH_1234
+        #     Date:                         Tue, 05 Mar 2013 16:50:52 GMT
+        #     X-Account-Bytes-Used:         0 (0.00 Bytes)
+        #     X-Account-Container-Count:    0
+        #     X-Account-Object-Count:       0
+        #
+        # Now let's change the account
+        #
+        #     service.change_account('AUTH_3333')
+        #     service.request :method => 'HEAD'
+        # 
+        # Would return something like:
+        #     
+        #     Account:                      AUTH_3333
+        #     Date:                         Tue, 05 Mar 2013 16:51:53 GMT
+        #     X-Account-Bytes-Used:         23423433
+        #     X-Account-Container-Count:    2
+        #     X-Account-Object-Count:       10
+        #
+        # If we wan't to go back to our original admin account:
+        #
+        #     service.reset_account_name
+        # 
+        def change_account(account)
+          @original_path ||= @path 
+          version_string = @path.split('/')[1]
+          @path = "/#{version_string}/#{account}"
+        end
+
+        def reset_account_name
+          @path = @original_path
+        end
+
         def request(params, parse_json = true, &block)
           begin
             response = @connection.request(params.merge({

tests/openstack/storage_tests.rb

@@ -0,0 +1,19 @@
+Shindo.tests('Fog::Storage[:openstack]', ['openstack', 'storage']) do
+
+  storage = Fog::Storage[:openstack]
+  original_path = storage.instance_variable_get :@path
+
+  tests("account changes") do
+    test("#change_account") do
+      new_account = 'AUTH_1234567890'
+      storage.change_account new_account
+      storage.instance_variable_get(:@path) != original_path
+    end
+    test("#reset_account_name") do
+      storage.reset_account_name
+      storage.instance_variable_get(:@path) == original_path
+    end
+  end
+
+end
+