Define DEST in stackrc

Move the initial definition of DEST so it is available in localrc and
the tools/*.sh scripts.

Change-Id: Ifc1b3cf3c3cd7b732007e83e74710f14f20f7624
diff --git a/stackrc b/stackrc
index 3a19cdb..55101de 100644
--- a/stackrc
+++ b/stackrc
@@ -1,6 +1,9 @@
 # Find the other rc files
 RC_DIR=$(cd $(dirname "$BASH_SOURCE") && pwd)
 
+# Destination path for installation
+DEST=/opt/stack
+
 # Specify which services to launch.  These generally correspond to
 # screen tabs. If you like to add other services that are not enabled
 # by default you can append them in your ENABLED_SERVICES variable in