[calico-containers] Align to upstream

s/BUILD_CONTAINER_NAME/PYTHON_BUILD_CONTAINER_NAME

[1]. https://github.com/projectcalico/calico-containers/commit/7a4afcbc7ae1d7d0dd02129cbe079346af9681c3

Change-Id: I42bea7d6c7ac3d32141ba8d63c85cb46a43af219
diff --git a/vars/buildCalicoContainers.groovy b/vars/buildCalicoContainers.groovy
index 9c4e53f..d62aadb 100644
--- a/vars/buildCalicoContainers.groovy
+++ b/vars/buildCalicoContainers.groovy
@@ -47,7 +47,7 @@
     sh """
       make calico/ctl \
         CTL_CONTAINER_NAME=${ctlContainerName} \
-        BUILD_CONTAINER_NAME=${buildImage} \
+        PYTHON_BUILD_CONTAINER_NAME=${buildImage} \
         BIRDCL_URL=${birdclUrl}
     """
   }
@@ -57,7 +57,7 @@
     sh """
       make calico/node \
         NODE_CONTAINER_NAME=${nodeContainerName} \
-        BUILD_CONTAINER_NAME=${buildImage} \
+        PYTHON_BUILD_CONTAINER_NAME=${buildImage} \
         FELIX_CONTAINER_NAME=${felixImage} \
         CONFD_URL=${confdUrl} \
         BIRD_URL=${birdUrl} \