Bug 20757: Capture and upload screenshot on selenium errors

Bug 20757: Capture and upload screenshot on selenium errors

It is a real pain to debug selenium errors, especially when it is
not reproducible locally.

This patch capture a screenshot when an error occurred and upload it
using the excellent lut.im service provided by framasoft
(We could host our own later).

Test plan:
Modify a selenium script to make it fails (search for find_element)
You will see a stack trace followed by a link to framapic.org

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>