[users at bb.net] buildbot 1.2.1-ish: reconfig stops but doesn't stop builds?

[Dan Kegel]

I've always been leery of doing 'buildbot reconfig' while builds are running,
but I did it accidentally just now.  Result?  The builds became zombies,
but the master thought they were still going.

I clicked stop again for good measure, didn't help.

For what it's worth, the log shows:

2018-08-08 18:28:08-0700
[_GenericHTTPChannelProtocol,4747,10.18.112.18]  <Build
mezzanine-mz-try-ubu1604 number:111 results:retry>: stopping build: no
reason 6
2018-08-08 18:28:08-0700
[_GenericHTTPChannelProtocol,4747,10.18.112.18]
RemoteCommand.interrupt <RemoteShellCommand '['bau', '-v',
'package']'> no reason
2018-08-08 18:28:08-0700
[_GenericHTTPChannelProtocol,4747,10.18.112.18]  but this
RemoteCommand is already inactive
2018-08-08 18:28:08-0700
[_GenericHTTPChannelProtocol,4747,10.18.112.18] Got fatal Exception on
DB
        Traceback (most recent call last):
          File "/home/buildbot/.local/lib/python3.6/site-packages/twisted/python/threadpool.py",
line 266, in <lambda>
            inContext.theWork = lambda: context.call(ctx, func, *args, **kw)
          File "/home/buildbot/.local/lib/python3.6/site-packages/twisted/python/context.py",
line 122, in callWithContext
            return self.currentContext().callWithContext(ctx, func, *args, **kw)
          File "/home/buildbot/.local/lib/python3.6/site-packages/twisted/python/context.py",
line 85, in callWithContext
            return func(*args,**kw)
          File "/home/buildbot/.local/lib/python3.6/site-packages/buildbot-1.2.1.dev66-py3.6.egg/buildbot/db/pool.py",
line 210, in __thd
            log.err(e, 'Got fatal Exception on DB')
        --- <exception caught here> ---
          File "/home/buildbot/.local/lib/python3.6/site-packages/buildbot-1.2.1.dev66-py3.6.egg/buildbot/db/pool.py",
line 184, in __thd
            rv = callable(arg, *args, **kwargs)
          File "/home/buildbot/.local/lib/python3.6/site-packages/buildbot-1.2.1.dev66-py3.6.egg/buildbot/db/logs.py",
line 157, in thdAddLog
            "log with slug '%r' already exists in this step" % (slug,))
        builtins.KeyError: "log with slug ''cancelled'' already exists
in this step"

$ buildbot --version
Buildbot version: 1.2.1-dev66
Twisted version: 18.4.0

This is from late may,
v1.2.0-60-gfacc54044
plus a couple gitlab patches.
- Dan