Add castellan to LIBS_FROM_GIT

Allow castellan to be installed from git instead of pip.

Castellan has recently been moved under the oslo framework,
and the barbican-tempest-plugin tests which use castellan
would benefit from the ability to usd castellan from git
instead of pip.

Change-Id: I96edca90c61aec84637b7b1ce842eff04c521923
diff --git a/stackrc b/stackrc
index 88f7541..72ad52d 100644
--- a/stackrc
+++ b/stackrc
@@ -364,6 +364,10 @@
 #
 ###################
 
+# castellan key manager interface
+GITREPO["castellan"]=${CASTELLAN_REPO:-${GIT_BASE}/openstack/castellan.git}
+GITBRANCH["castellan"]=${CASTELLAN_BRANCH:-master}
+
 # cliff command line framework
 GITREPO["cliff"]=${CLIFF_REPO:-${GIT_BASE}/openstack/cliff.git}
 GITBRANCH["cliff"]=${CLIFF_BRANCH:-master}