Move migration to run after post-configure

This change has been discussed and planned for a while. We have not used
migrations much in TripleO, so it was not clear that it was necessary.
But as we move to HA deployments we need a way to run scripts after the
system state has been asserted, which is what migration is for.

Change-Id: I16d90abb3fccc791001beb5d8ed267fcd00f820c

README.rst

@@ -7,8 +7,8 @@ pre-defined set of directories::
 
   /opt/stack/os-config-refresh/pre-configure.d
   /opt/stack/os-config-refresh/configure.d
-  /opt/stack/os-config-refresh/migration.d
   /opt/stack/os-config-refresh/post-configure.d
+  /opt/stack/os-config-refresh/migration.d
 
 `/opt/stack/os-config-refresh` is the default base directory. You can
 set `OS_REFRESH_CONFIG_BASE_DIR` environment variable to override the
@@ -18,10 +18,18 @@ Its intended purpose is to separate scripts execution into 4 phases:
 
 1. Quiesce(pre-configure.d),
 2. Configure(configure.d),
-3. Migrate(migration.d),
-4. Activate(post-configure.d).
+3. Activate(post-configure.d).
+4. Migrate(migration.d),
 
 It runs through all the phases above to ensure configuration is
 applied and enabled on a machine. It will exit with an error if any
 phase has a problem. The scripts in each phase should not depend on
 each other having worked properly.
+
+Note: Earlier versions of os-refresh-config ran migration before
+post-configure. This was an oversight in the initial design, as
+migrations are intended to be online migrations after the host is
+fully configured.
+
+For things which must happen while the service is quiesced, that should
+be done in the post-configure scripts which control the service state.

os_refresh_config/os_refresh_config.py

@@ -26,8 +26,8 @@ BASE_DIR = os.environ.get('OS_REFRESH_CONFIG_BASE_DIR',
                           '/opt/stack/os-config-refresh')
 PHASES = ['pre-configure',
           'configure',
-          'migration',
-          'post-configure']
+          'post-configure',
+          'migration']
 
 
 def main(argv=sys.argv):