zdtm: fix a lint warning

$ make lint
flake8 --config=scripts/flake8.cfg test/zdtm.py
test/zdtm.py:323:19: F841 local variable 'e' is assigned to but never used
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

test/zdtm.py

@@ -314,6 +314,8 @@ def wait_pid_die(pid, who, tmo = 30):
 		try:
 			os.kill(int(pid), 0)
 		except OSError, e:
+			if e.errno != errno.ESRCH:
+				print e
 			break
 
 		print "Wait for %s(%d) to die for %f" % (who, pid, stime)