Adds failure message to _got_response_2
Removes extra +1 to number of servers contacted
Reworks test_lost_servers test in test_download.py

While the previous algorithm would reliably distribute shares
in increasing order to the trackers, Upload of Happiness doesn't do
this. This causes the finder to query for a random set of shares based
on the order shares are allocated by the uploader. In order for the
finder to have a reproducible behavior, the finder must sort servers
by their server id because Upload of Happiness tracks servers by server
id in a set.

test_lost_servers is modified to reflect the different set of shares
the new finder will reliably reproduce.