swrap: Fix loading of system libraries.
torture: Let the echo server listen on anyaddr.
torture: Add torture_server_address().

This should make it easier to run the test without socket_wrapper.
torture: Add torture_server_port().
tests: Use torture_server_(address|port).

This makes it possible to run tests without socket_wrapper.
tests: Add test_echo_tcp_write_readv
tests: Add an ifdef around static IPv6 only functions

This would prevent an uninitialized function warning in case IPv6 was not
available.