LP #1070434: pt-stalk --no-stalk and --iterations 1 don't wait for the collect

**Reported in Launchpad by Daniel Nichter last update 16-11-2012 00:08:50

A pt-stalk does:

$trunk/bin/pt-stalk --iterations 1 --dest $dest --variable Uptime --threshold $threshold --cycles 2 --run-time 2 --pid $pid_file – --defaults-file=$cnf >$log_file 2>&1

It means to test --run-time, but it was failing sporadically. Turns out, on fast systems (a rare case where being slow actually makes the test work) pt-stalk runs, triggers, collect subprocess starts, then pt-stalk exists because there's no more iterations. When the tool exists, it kills the collect subprocess, so nothing is collected.