Update diskimage-builder's URL

diskimage-builder has moved from stackforge to openstack.

Change-Id: I5bc8d5d162d7d671e062efd67992f15fbb4307b2
diff --git a/stackrc b/stackrc
index 3a338d1..5c0baf7 100644
--- a/stackrc
+++ b/stackrc
@@ -160,7 +160,7 @@
 
 
 # diskimage-builder
-BM_IMAGE_BUILD_REPO=${BM_IMAGE_BUILD_REPO:-${GIT_BASE}/stackforge/diskimage-builder.git}
+BM_IMAGE_BUILD_REPO=${BM_IMAGE_BUILD_REPO:-${GIT_BASE}/openstack/diskimage-builder.git}
 BM_IMAGE_BUILD_BRANCH=${BM_IMAGE_BUILD_BRANCH:-master}
 
 # bm_poseur