Always include WebDriver process liveness in http client exception

[lread]

Currently

We use slingshot to throw+ on HTTP exceptions.
This map we throw includes the :driver which includes the WebDriver :process.

While poking around #464 and #465 I found I wanted to also report if the WebDriver process is running and if not, its exit code.

Proposal

Adjust our http client to slingshot throw+ also on unexpected exceptions (ex. timeouts).
Include unexpected exception as cause.

When :driver includes :process check if it is alive.
If not then realize its exit code and include it under and updated :process.