Fix that DISTRO is not set in unstack.sh

Change-Id: I36cab41fdb767e8e31073a4fa1f929090f702910
Closes-Bug: #1738938

unstack.sh

@@ -45,6 +45,10 @@ fi
 # Configure Projects
 # ==================
 
+# Determine what system we are running on.  This provides ``os_VENDOR``,
+# ``os_RELEASE``, ``os_PACKAGE``, ``os_CODENAME`` and ``DISTRO``
+GetDistro
+
 # Plugin Phase 0: override_defaults - allow plugins to override
 # defaults before other services are run
 run_phase override_defaults
@@ -83,10 +87,6 @@ fi
 
 load_plugin_settings
 
-# Determine what system we are running on.  This provides ``os_VENDOR``,
-# ``os_RELEASE``, ``os_PACKAGE``, ``os_CODENAME``
-GetOSVersion
-
 set -o xtrace
 
 # Run extras