allow passing additional options to graphviz, fix #332

[badiku]

allow passing additional options to graphviz, fix #332

[martindurant]

Unfortunately, this breaks current usage (see the test failure), where the passed kwarg was expected to be already graph_attr. To allow both old and new usage, you could see if any of the top-level kwargs are in the passed dict,
{'name',
'comment',
'filename',
'directory',
'format',
'engine',
'encoding',
'graph_attr',
'node_attr',
'edge_attr',
'body',
'strict'}
and if not, set
graph_attr = {'graph_attr': graph_attr}.
I would use set intersection to see if there are any top-level keys.

[badiku]

streamz/tests/test_kafka.py::test_kafka_checkpointing_auto_offset_reset_latest FAILED [ 99%]

test_kafka_checkpointing_auto_offset_reset_latest faild? don't know why.

def launch_kafka():
   ...
   wait_for(predicate, 10, period=0.1)
   ...

streamz/tests/test_kafka.py:592: 
wait_for(lambda: len(out1) == 3 and (len(out1[0]) + len(out1[1]) + len(out1[2])) == 30, 10, 0.1)

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
predicate = <function test_kafka_checkpointing_auto_offset_reset_latest.<locals>.<lambda> at 0x7f4fb8b33670>
timeout = 10, fail_func = 0.1, period = 0.001
    def wait_for(predicate, timeout, fail_func=None, period=0.001):
        """Wait for predicate to turn true, or fail this test"""
        # from distributed.utils_test
        deadline = time() + timeout
        while not predicate():
            sleep(period)
            if time() > deadline:  # pragma: no cover
                if fail_func is not None:
>                   fail_func()
E                   TypeError: 'float' object is not callable
streamz/utils_test.py:115: TypeError

so some code at streamz/tests/test_kafka.py:592 send wrong arguments to wait_for function,
fail_func got float 0.1 but should be callable?

but I did not touch this kafka part.

[martindurant]

Try to just run it again (push an empty commit if you have to). The kafka tests have sometimes become flaky, but we don't know why.