Add nova-status upgrade check command framework

This adds the basic framework for the nova-status
upgrade check commands. Follow up patches will flesh
this out to perform cells v2 and placement API related
upgrade status checks.

A man page is added for the new CLI and as part of that
the man page index is sorted.

Part of blueprint cells-scheduling-interaction
Part of blueprint resource-providers-scheduler-db-filters

Change-Id: I687dd7317703a1bb76c197ebba849ca368c0872e

setup.cfg

@@ -67,6 +67,7 @@ console_scripts =
     nova-scheduler = nova.cmd.scheduler:main
     nova-serialproxy = nova.cmd.serialproxy:main
     nova-spicehtml5proxy = nova.cmd.spicehtml5proxy:main
+    nova-status = nova.cmd.status:main
     nova-xvpvncproxy = nova.cmd.xvpvncproxy:main
 wsgi_scripts =
     nova-placement-api = nova.api.openstack.placement.wsgi:init_application