Can set node-specific nick bases

With the 'nick_base' option, you can specify what string the nick
should begin with. The default is 'test', which is the string that
chutney used previously.

lib/chutney/TorNet.py

@@ -1090,6 +1090,7 @@ DEFAULTS = {
     'num_cpus': None,
     'numa_settings': None,
     'measureme_log_dir': '${dir}',
+    'nick_base': 'test',
     'valgrind_settings': None,
 }
 
@@ -1168,7 +1169,7 @@ class TorEnviron(chutney.Templating.Environ):
                                                 my['nodenum'], my['tag'])))
 
     def _get_nick(self, my):
-        return "test%03d%s" % (my['nodenum'], my['tag'])
+        return "%s%03d%s" % (my['nick_base'], my['nodenum'], my['tag'])
 
     def _get_tor_gencert(self, my):
         return my['tor-gencert'] or '{0}-gencert'.format(my['tor'])