ctdb-daemon: Fix valgrind hit in event code

ctdb-daemon: Fix valgrind hit in event code

==25741== Syscall param write(buf) points to uninitialised byte(s)
==25741==    at 0x4939291: write (write.c:27)
==25741==    by 0x4868285: sys_write (sys_rw.c:68)
==25741==    by 0x13915D: sock_queue_trigger (sock_io.c:316)
==25741==    by 0x4DE6478: tevent_common_invoke_immediate_handler (in /usr/lib/x86_64-linux-gnu/libtevent.so.0.9.37)
==25741==    by 0x4DE64A2: tevent_common_loop_immediate (in /usr/lib/x86_64-linux-gnu/libtevent.so.0.9.37)
==25741==    by 0x4DEBE5A: ??? (in /usr/lib/x86_64-linux-gnu/libtevent.so.0.9.37)
==25741==    by 0x4DEA2D6: ??? (in /usr/lib/x86_64-linux-gnu/libtevent.so.0.9.37)
==25741==    by 0x4DE57E3: _tevent_loop_once (in /usr/lib/x86_64-linux-gnu/libtevent.so.0.9.37)
==25741==    by 0x15D1BA: ctdb_event_script_args (eventscript.c:821)
==25741==    by 0x13B437: ctdb_start_daemon (ctdb_daemon.c:1315)
==25741==    by 0x110642: main (ctdbd.c:393)
==25741==  Address 0x57888a4 is 100 bytes inside a block of size 144 alloc'd
==25741==    at 0x48357BF: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==25741==    by 0x4B9B7C0: talloc_named_const (in /usr/lib/x86_64-linux-gnu/libtalloc.so.2.1.14)
==25741==    by 0x15CCC6: eventd_client_write (eventscript.c:430)
==25741==    by 0x15CCC6: eventd_client_run (eventscript.c:556)
==25741==    by 0x15CCC6: ctdb_event_script_run (eventscript.c:649)
==25741==    by 0x15D198: ctdb_event_script_args (eventscript.c:812)
==25741==    by 0x13B437: ctdb_start_daemon (ctdb_daemon.c:1315)
==25741==    by 0x110642: main (ctdbd.c:393)
==25741==

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13659

Pair-programmed-with: Amitay Isaacs <amitay@gmail.com>
Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>
Autobuild-User(master): Amitay Isaacs <amitay@samba.org>
Autobuild-Date(master): Mon Oct 22 09:27:15 CEST 2018 on sn-devel-144

(cherry picked from commit fbea9d36996f248ba2b077f12ad16c199b853134)

Autobuild-User(v4-9-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-9-test): Thu Oct 25 11:05:48 CEST 2018 on sn-devel-144