[cwctl] on upgrade, clear instance_md5_version cache The generate-static-datadir depends on a correct config.instance_md5_version(), and we just invalidated it by upgrading the instance.

[twisted] add request error handler to avoid finishing it twice And avoid stack traces like:: Traceback (most recent call last): File "/usr/lib/python2.7/threading.py", line 783, in __bootstrap self.__bootstrap_inner() File "/usr/lib/python2.7/threading.py", line 810, in __bootstrap_inner self.run() File "/usr/lib/python2.7/threading.py", line 763, in run self.__target(*self.__args, **self.__kwargs) --- <exception caught here> --- [...] File "/usr/lib/python2.7/dist-packages/twisted/python/threadpool.py", line 196, in _worker result = context.call(ctx, function, *args, **kwargs) File "/usr/lib/python2.7/dist-packages/twisted/python/context.py", line 118, in callWithContext return self.currentContext().callWithContext(ctx, func, *args, **kw) File "/usr/lib/python2.7/dist-packages/twisted/python/context.py", line 81, in callWithContext return func(*args,**kw) File "/home/me/envs/grshell-cw/cubicweb/statsd_logger.py", line 121, in __call__ return self.callable(*args, **kw) File "/home/me/envs/grshell-cw/cubicweb/etwist/server.py", line 131, in render_request code=500, twisted_request=request) File "/home/me/envs/grshell-cw/cubicweb/etwist/http.py", line 22, in __init__ self._finalize() File "/home/me/envs/grshell-cw/cubicweb/etwist/http.py", line 46, in _finalize self._twreq.finish() File "/usr/lib/python2.7/dist-packages/twisted/web/server.py", line 228, in finish return http.Request.finish(self) File "/usr/lib/python2.7/dist-packages/twisted/web/http.py", line 931, in finish "Request.finish called on a request after its connection was lost; " exceptions.RuntimeError: Request.finish called on a request after its connection was lost; use Request.notifyFinish to keep track of this.