Add SERVICE_TOKEN to the sample local.conf

I expect the sample local.conf file to contain all the required
variables. However, after copying samples/local.conf, the stack.sh
script still asks for SERVICE_TOKEN.

This commit adds the SERVICE_TOKEN definition to local.conf so that a
new user can just copy samples/local.conf, edit it, and have a running
stack.sh without the mild annoyance of having more variables to set.

Change-Id: Ifb163c7f67c80037d8b10458f2df458a20da4667
diff --git a/samples/local.conf b/samples/local.conf
index c8126c2..20c5892 100644
--- a/samples/local.conf
+++ b/samples/local.conf
@@ -24,8 +24,10 @@
 # While ``stack.sh`` is happy to run without ``localrc``, devlife is better when
 # there are a few minimal variables set:
 
-# If the ``*_PASSWORD`` variables are not set here you will be prompted to enter
-# values for them by ``stack.sh`` and they will be added to ``local.conf``.
+# If the ``SERVICE_TOKEN`` and ``*_PASSWORD`` variables are not set
+# here you will be prompted to enter values for them by ``stack.sh``
+# and they will be added to ``local.conf``.
+SERVICE_TOKEN=azertytoken
 ADMIN_PASSWORD=nomoresecrete
 MYSQL_PASSWORD=stackdb
 RABBIT_PASSWORD=stackqueue