Component.start() - loop argument is not propagated properly

Consider the following:

import asyncio
from autobahn.asyncio.component import Component

comp = Component()
loop = asyncio.new_event_loop()
f = comp.start(loop=loop)
print("passed loop id = ", id(loop))
print("retruned loop id = ", id(f._loop))
print("default loop id = ", id(asyncio.get_event_loop()))

Which results in

passed loop id =  140480361130696
retruned loop id =  140480298199416
default loop id =  140480298199416

I.e. somewhere down the road, Autobahn falls back to use the default loop.

It breaks on us while trying to run tests using asynctest module which tries to provide isolated loop for each test. For now we get away with setting use_default_loop to False, which is not ideal of course.

Start in autobahn.asyncio.component at Component.start() and trace how the supplied loop reaches the returned future. Reproduce the issue with the Python snippet and compare f._loop with the explicitly passed loop and the default loop. Done means the returned future uses the loop passed to Component.start(), including when isolated asynctest loops are used.