ctdb-scripts: Call iptables/ip6tables directly from iptables_wrapper

ctdb-scripts: Call iptables/ip6tables directly from iptables_wrapper

Drops the iptables() and ip6tables() functions and, hence, the
hardcoding of paths /sbin/iptables and /sbin/ip6tables.  The latter
avoids problems on openSUSE where (for example) /usr/sbin/iptables is
used instead.

This means that locking around ip*tables commands is only done when
iptables_wrapper is called directly.  This is fine because the only
conflict is when "releaseip" or "takeip"/"updateip" events are run in
parallel.  The other uses in 11.natgw and 70.iscsi are in events where
there will be no collisions.

Making 11.natgw support IPv6 is unnecessary.  Just put a static IPv6
address on each interface - they're plentiful.

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): Wed Jan 28 08:29:55 CET 2015 on sn-devel-104

(cherry picked from commit ab51f283e7a7f4fc82a94d39e7bb3a68e8aac554)

The last 2 patches address

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11203

CTDB has some remaining IPv6-related issues.