key_generator: remove poll timeouts from test

key_generator: remove poll timeouts from test

the timeouts on uses of 'poll' were there purely to make sure a test doesn't
poll indefinitely.  however having such timeouts makes tests susceptible
to premature timeouts under high load, or on slow machines. (e.g. cygwin
slaves running in virtual machines on loaded hosts)

purportedly trial by default applies a timeout to tests to prevent them
hanging out indefinitely, so these poll timeouts are redundant and cause
intermittent failures on slow hosts.  hence they're more bother than they're
worth, and should be culled.