Separate opt registration from command running

In some scenarios, it is useful for the caller of upgradecheck
to be responsible for parsing the conf (see [1]). Since
registering command line options must come before parsing,
we must separate registation from running the commands.

This change enables that by making `register_cli_options` public
and extracting a public `run` method. `main` continues to work
as before by calling these new methods.

[1] I2eea00343d1bbdf486985daeaf6707358b6a2708

Change-Id: I3d7e28d2432f5b04d4154793025786dc289b0cb2

oslo_upgradecheck/upgradecheck.py

@@ -141,7 +141,7 @@ class UpgradeCommands(object):
         return return_code
 
 
-def _register_cli_options(conf, upgrade_command):
+def register_cli_options(conf, upgrade_command):
     """Set up the command line options.
 
     Adds a subcommand to support 'upgrade check' on the command line.
@@ -156,6 +156,16 @@ def _register_cli_options(conf, upgrade_command):
     conf.register_cli_opt(opt)
 
 
+def run(conf):
+    """Run the requested command."""
+    try:
+        return conf.command.action_fn()
+    except Exception:
+        print(_('Error:\n%s') % traceback.format_exc())
+        # This is 255 so it's not confused with the upgrade check exit codes.
+        return 255
+
+
 def main(conf, project, upgrade_command,
          argv=sys.argv[1:],
          default_config_files=None):
@@ -177,7 +187,7 @@ def main(conf, project, upgrade_command,
                                  the search behavior in oslo.config.
 
     """
-    _register_cli_options(conf, upgrade_command)
+    register_cli_options(conf, upgrade_command)
 
     conf(
         args=argv,
@@ -185,9 +195,4 @@ def main(conf, project, upgrade_command,
         default_config_files=default_config_files,
     )
 
-    try:
-        return conf.command.action_fn()
-    except Exception:
-        print(_('Error:\n%s') % traceback.format_exc())
-        # This is 255 so it's not confused with the upgrade check exit codes.
-        return 255
+    return run(conf)