Update vagrant files with rc4 images.

vagrant/release/devstack/Vagrantfile

@@ -93,9 +93,12 @@ openedx_releases = {
   "named-release/cypress.rc3" => {
     :name => "cypress-devstack-rc3", :file => "20150724-cypress-devstack-rc3.box",
   },
+  "named-release/cypress.rc4" => {
+    :name => "cypress-devstack-rc4", :file => "cypress-rc4-devstack.box",
+  },
 }
 openedx_releases.default = {
-  :name => "cypress-devstack-rc3", :file => "20150724-cypress-devstack-rc3.box",
+  :name => "cypress-devstack-rc4", :file => "cypress-rc4-devstack.box",
 }
 openedx_releases_vmware = {
   "named-release/birch" => {

vagrant/release/fullstack/Vagrantfile

@@ -39,9 +39,12 @@ openedx_releases = {
   "named-release/cypress.rc3" => {
     :name => "cypress-fullstack-rc3", :file => "20150724-cypress-fullstack-rc3.box",
   },
+  "named-release/cypress.rc4" => {
+    :name => "cypress-fullstack-rc4", :file => "cypress-rc4-fullstack.box",
+  },
 }
 openedx_releases.default = {
-  :name => "cypress-fullstack-rc3", :file => "20150724-cypress-fullstack-rc3.box",
+  :name => "cypress-fullstack-rc4", :file => "cypress-rc4-fullstack.box",
 }
 openedx_releases_vmware = {
   "named-release/birch" => {