Retry _configure_option to fix IOError caused by not-ready sys files

[troelsim]

Address #1 by retrying _configure_option 3 times before aborting.
If it fails first time, try again after 20 ms, then again after 5*20ms = 100 ms.

[sardok]

Thanks @troelsim for the PR. I think, it would better if we keep the asynchronous nature of the library here.

See discussion here: http://twistedmatrix.com/pipermail/twisted-python/2015-December/030041.html