Support timestamps as prefixes for traceback log lines.

Traceback lines in the log are now formatted to match other log
lines. So, instead of getting something like:

2012-03-26 14:53:26 ERROR nova.rpc.common [-] AMQP server on 10.55.58.1:5672 is unreachable: Socket closed. Trying again in 1 secon
ds.
(nova.rpc.common): TRACE: Traceback (most recent call last):
(nova.rpc.common): TRACE:   File "/usr/lib/python2.7/dist-packages/nova/rpc/impl_kombu.py", line 446, in reconnect
(nova.rpc.common): TRACE:     self._connect()
(nova.rpc.common): TRACE:   File "/usr/lib/python2.7/dist-packages/nova/rpc/impl_kombu.py", line 423, in _connect
(nova.rpc.common): TRACE:     self.connection.connect()
[snip]

You would get something like:

2012-03-26 14:53:26 ERROR nova.rpc.common [-] AMQP server on 10.55.58.1:5672 is unreachable: Socket closed. Trying again in 1 secon
ds.
2012-03-26 14:53:26 TRACE nova.rpc.common Traceback (most recent call last):
2012-03-26 14:53:26 TRACE nova.rpc.common   File "/usr/lib/python2.7/dist-packages/nova/rpc/impl_kombu.py", line 446, in reconnect
2012-03-26 14:53:26 TRACE nova.rpc.common     self._connect()
2012-03-26 14:53:26 TRACE nova.rpc.common   File "/usr/lib/python2.7/dist-packages/nova/rpc/impl_kombu.py", line 423, in _connect
2012-03-26 14:53:26 TRACE nova.rpc.common     self.connection.connect()
[snip]

This is tracked by bug 967842.

Change-Id: Ie017317f7e0b636016a220cb21a3543ab569dea5

nova/log.py

@@ -63,7 +63,7 @@
                        '%(pathname)s:%(lineno)d',
                help='data to append to log format when level is DEBUG'),
     cfg.StrOpt('logging_exception_prefix',
-               default='(%(name)s): TRACE: ',
+               default='%(asctime)s TRACE %(name)s %(instance)s',
                help='prefix each line of exception output with this format'),
     cfg.StrOpt('instance_format',
                default='[instance: %(uuid)s] ',
@@ -247,11 +247,16 @@ def formatException(self, exc_info, record=None):
         """Format exception output with FLAGS.logging_exception_prefix."""
         if not record:
             return logging.Formatter.formatException(self, exc_info)
+
         stringbuffer = cStringIO.StringIO()
         traceback.print_exception(exc_info[0], exc_info[1], exc_info[2],
                                   None, stringbuffer)
         lines = stringbuffer.getvalue().split('\n')
         stringbuffer.close()
+
+        if FLAGS.logging_exception_prefix.find('%(asctime)') != -1:
+            record.asctime = self.formatTime(record, self.datefmt)
+
         formatted_lines = []
         for line in lines:
             pl = FLAGS.logging_exception_prefix % record.__dict__