BUG/MINOR: server: Don't warn fallback IP is used during init-addr resolution

BUG/MINOR: server: Don't warn fallback IP is used during init-addr resolution

When a fallback IP address is provided in the list of methods to use to
resolve the server address, a warning is emitted if previous methods
failed. The aim is to inform this address will be used for the
server. However, it is valid use-case. It is the expected behavior. There is
no reason to emit a warning. Having a message during HAProxy startup to
inform the fallback IP address will be used is probably a good idea. But it
should be a notice not a warning. Otherwise, checking the configuration
validity will always failed, just like starting HAProxy in zero-warning
mode while the option was set on purpose.

This patch should fix the issue #2627. It must be backported to all stable
versions.