Source functions from stackrc

stackrc now requires GITREPO, GITBRANCH, GITDIR and has been
dependent on functions for a while (is_package_installed).  Ensure
we source the required functions file when stackrc is loaded.  Avoids
unexpected issues in grenade where they may or may not have been loaded
depending on the configuration.

Closes-bug: #1377274

Change-Id: I5027cfad07af0de7ff39f424601d6f7ec5dcadae
diff --git a/stackrc b/stackrc
index 15f7f82..13b2e22 100644
--- a/stackrc
+++ b/stackrc
@@ -3,6 +3,9 @@
 # Find the other rc files
 RC_DIR=$(cd $(dirname "${BASH_SOURCE:-$0}") && pwd)
 
+# Source required devstack functions and globals
+source $RC_DIR/functions
+
 # Destination path for installation
 DEST=/opt/stack