trinity: Proxied services now record remote exceptions' tracebacks

[gsalgado]

Closes: #956

[pipermerriam]

naming nitpick

maybe TracebackPreserver or TracebackRecorder?

[cburgdorf]

👍 on TracebackRecorder

[pipermerriam]

maybe lift this out of the function body to the top level of the module and then this function body would be

if not inspect.ismethod(attr):
    return attr
else:
    return record_traceback_on_error(attr)

[gsalgado]

I've improved this a bit based on this trick

It uses exception chaining, which means we don't need any extra hacks to special case the logging of those exceptions. This is how it looks like:

   ERROR  07-11 11:45:15     service  Unexpected error in <p2p.chain.FastChainSyncer object at 0x7f7fa2b3cf60>, exiting
trinity.chains.RemoteTraceback:
"""
Traceback (most recent call last):
  File "/home/salgado/src/py-evm/trinity/chains/__init__.py", line 176, in wrapper
    return attr(*args, **kwargs)
  File "/home/salgado/src/py-evm/evm/db/header.py", line 86, in get_canonical_block_hash
    validate_block_number(block_number, title="Block Number")
  File "/home/salgado/src/py-evm/evm/validation.py", line 201, in validate_block_number
    validate_is_integer(block_number, title="Block Number")
  File "/home/salgado/src/py-evm/evm/validation.py", line 37, in validate_is_integer
    "{title} must be a an integer.  Got: {0}".format(type(value), title=title)
evm.exceptions.ValidationError: Block Number must be a an integer.  Got: <class 'bytes'>
"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/salgado/src/py-evm/p2p/service.py", line 55, in run
    await self._run()
  File "/home/salgado/src/py-evm/p2p/chain.py", line 120, in _run
    await self.wait(self.db.coro_get_canonical_block_hash(b'foo'))
  File "/home/salgado/src/py-evm/p2p/cancel_token.py", line 102, in wait
    return await self.wait_first(awaitable, token=token, timeout=timeout)
  File "/home/salgado/src/py-evm/p2p/cancel_token.py", line 123, in wait_first
    return await wait_with_token(*awaitables, token=token_chain, timeout=timeout)
  File "/home/salgado/src/py-evm/p2p/cancel_token.py", line 160, in wait_with_token
    return done.pop().result()
  File "/home/salgado/src/py-evm/trinity/utils/mp.py", line 27, in method
    args,
  File "/usr/lib/python3.6/concurrent/futures/thread.py", line 56, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/usr/lib/python3.6/multiprocessing/managers.py", line 772, in _callmethod
    raise convert_to_error(kind, result)
evm.exceptions.ValidationError: Block Number must be a an integer.  Got: <class 'bytes'>