ctdb-tests: Add some testing for IPv4-mapped IPv6 address parsing

ctdb-tests: Add some testing for IPv4-mapped IPv6 address parsing

ctdb_sock_addr values are hashed in some contexts.  This means that
all of the memory used for the ctdb_sock_addr should be consistent
regardless of how parsing is done.  The first 2 cases are just sanity
checks but the 3rd case involving an IPv4-mapped IPv6 address is the
real target of this test addition.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13839

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@samba.org>