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/lib/oslo b/lib/oslo
index 1a78bdf..182295c 100644
--- a/lib/oslo
+++ b/lib/oslo
@@ -23,6 +23,7 @@
 # Defaults
 # --------
 GITDIR["automaton"]=$DEST/automaton
+GITDIR["castellan"]=$DEST/castellan
 GITDIR["cliff"]=$DEST/cliff
 GITDIR["debtcollector"]=$DEST/debtcollector
 GITDIR["futurist"]=$DEST/futurist
@@ -71,6 +72,7 @@
 # install_oslo() - Collect source and prepare
 function install_oslo {
     _do_install_oslo_lib "automaton"
+    _do_install_oslo_lib "castellan"
     _do_install_oslo_lib "cliff"
     _do_install_oslo_lib "debtcollector"
     _do_install_oslo_lib "futurist"