fix: support dual-stack ipv4 and ipv6 machines

[vlsi]

Previously, LISTEN_ADDR was set to hostname -i which might return multiple ip addresses separated with space, which is not compatible with cases like ${LISTEN_ADDR}:5432

When listen on all the addresses is needed, we'd better use *:5432

[vlsi]

It might be better to remove the variable LISTEN_ADDR so it is not accidentally used somewhere else since having a static * does not look helpful.

[vlsi]

Closing in favour of #33.

Here's a PR for the removal of LISTEN_ADDR usages: Netcracker/pgskipper-operator#103