Install sqlalchemy-migrate from master if requested

Added possibility to install sqlalchemy-migrate from master instead of
pypi packages.

Change-Id: I8af92cbb03609799442b05db9772e3c82b76725b
diff --git a/stackrc b/stackrc
index 4f955bd..ad7da6c 100644
--- a/stackrc
+++ b/stackrc
@@ -319,6 +319,10 @@
 PECAN_REPO=${PECAN_REPO:-${GIT_BASE}/stackforge/pecan.git}
 PECAN_BRANCH=${PECAN_BRANCH:-master}
 
+# sqlalchemy-migrate
+SQLALCHEMY_MIGRATE_REPO=${SQLALCHEMY_MIGRATE_REPO:-${GIT_BASE}/stackforge/sqlalchemy-migrate.git}
+SQLALCHEMY_MIGRATE_BRANCH=${SQLALCHEMY_MIGRATE_BRANCH:-master}
+
 
 # Nova hypervisor configuration.  We default to libvirt with **kvm** but will
 # drop back to **qemu** if we are unable to load the kvm module.  ``stack.sh`` can