api: support timeout kwarg to be handed down to requests

[awelzel]

Hi,

this pull request introduces support for a "timeout" keyword arg to be handed down to session.request().

It is good practice to use a timeout when using requests [1]. In fact, we have observed processes getting stuck forever in the session.request() call and had to regularly restart them. A new exception "Timeout" is added. It's the users responsibility to retry if this is required.
.
I'm happy to hear about suggestions or improvements.

Thanks,
Arne

[1] http://docs.python-requests.org/en/master/user/advanced/#timeouts

[awelzel]

Hey, any thoughts on this?

It would be nice to not maintain this out of tree :-)

[awelzel]

@brad ?

[brad]

@awelzel Looks great! Thank you so much for the tests!

[awelzel]

Thanks!