Re-run nova-manage under sudo if unable to read conffile

Having to manually sudo to the nova user to make things work is
tedious. Make it so that if we can't read the conffile, we just
re-exec under sudo.

Fixes bug 805695

Change-Id: I322cece80ca757c69147fb3f8474ad137d9bff82

bin/nova-manage

@@ -2307,7 +2307,16 @@ def methods_of(obj):
 
 def main():
     """Parse options and call the appropriate class/method."""
-    utils.default_flagfile()
+    flagfile = utils.default_flagfile()
+
+    if flagfile and not os.access(flagfile, os.R_OK):
+        st = os.stat(flagfile)
+        print "Could not read %s. Re-running with sudo" % flagfile
+        try:
+            os.execvp('sudo', ['sudo', '-u', '#%s' % st.st_uid] + sys.argv)
+        except:
+            print 'sudo failed, continuing as if nothing happened'
+
     argv = FLAGS(sys.argv)
     logging.setup()