Update KillFilter to stop at '\0' for readlink() function.

Python's readlink() implementation doesn't stop at '\0' when reading
file path. Thus after dnsmasq upgrade, it may return something like
'/usr/sbin/dnsmasq\03453 (deleted)', while C's or Shell's readlink()
return '/usr/sbin/dnsmasq'. This patch fixes this problem by cutting
the readlink() results with '\0', so that KillFilter could get correct
path.

Bug 1179793

Change-Id: I7354941e0508e019c8c9b63b87ad39f52ccb51ca
Merge "Update KillFilter to stop at '\0' for readlink() function."