I've dropped all "b" prefixes from the power states in provisioningserver/drivers/power/amt.py and now I'm seeing another error, which causes a similar power check errors. The new error is because apparently the AMT controller often responds with "500 Can't connect to <IP>", which is treated as PowerFatalError, but it shouldn't (as retrying usually works as expected - in my observations at least).

Here's the patch I used: http://paste.ubuntu.com/15810913/

The error I described earlier causes the following traceback in the rackd.log:

2016-04-13 16:22:15+0300 [ClusterClient,client] Failed to refresh power state.
        Traceback (most recent call last):
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 434, in errback
            self._startRunCallbacks(fail)
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 501, in _startRunCallbacks
            self._runCallbacks()
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 588, in _runCallbacks
            current.result = callback(current.result, *args, **kw)
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1184, in gotResult
            _inlineCallbacks(r, g, deferred)
        --- <exception caught here> ---
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1126, in _inlineCallbacks
            result = result.throwExceptionIntoGenerator(g)
          File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
            return g.throw(self.type, self.value, self.tb)
          File "/usr/lib/python3/dist-packages/provisioningserver/power/query.py", line 103, in get_power_state
            raise exc_type(exc_value).with_traceback(exc_trace)
          File "/usr/lib/python3/dist-packages/provisioningserver/power/query.py", line 92, in get_power_state
            system_id, hostname, power_type, context)
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1126, in _inlineCallbacks
            result = result.throwExceptionIntoGenerator(g)
          File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
            return g.throw(self.type, self.value, self.tb)
          File "/usr/lib/python3/dist-packages/provisioningserver/drivers/power/__init__.py", line 240, in query
            self.power_query, system_id, context)
          File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 246, in inContext
            result = inContext.theWork()
          File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 262, in <lambda>
            inContext.theWork = lambda: context.call(ctx, func, *args, **kw)
          File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 118, in callWithContext
            return self.currentContext().callWithContext(ctx, func, *args, **kw)
          File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 81, in callWithContext
            return func(*args,**kw)
          File "/usr/lib/python3/dist-packages/provisioningserver/drivers/power/amt.py", line 367, in power_query
            amt_command = self._get_amt_command(ip_address, power_pass)
          File "/usr/lib/python3/dist-packages/provisioningserver/drivers/power/amt.py", line 293, in _get_amt_command
            "Unable to retrieve AMT version: %s" % stderr)
        provisioningserver.drivers.power.PowerFatalError: Unable to retrieve AMT version: 500 Can't connect to 10.14.0.12:16992 at /usr/bin/amttool line 126.