added support to override THEMES_VERSION for sandbox creation

util/install/sandbox.sh

@@ -53,6 +53,7 @@ VERSION_VARS=(
   ECOMMERCE_VERSION
   ECOMMERCE_WORKER_VERSION
   DISCOVERY_VERSION
+  THEMES_VERSION
 )
 
 for var in ${VERSION_VARS[@]}; do

util/jenkins/ansible-provision.sh

@@ -190,6 +190,7 @@ xserver_version: $xserver_version
 certs_version: $certs_version
 configuration_version: $configuration_version
 demo_version: $demo_version
+THEMES_VERSION: $themes_version
 
 edx_ansible_source_repo: ${configuration_source_repo}
 edx_platform_repo: ${edx_platform_repo}