MINOR: server: detect name conflict earlier during parsing

MINOR: server: detect name conflict earlier during parsing

Since 3.3, server name unicity is strictly enforced, even in case of
different numerical IDs.

  d7fad1320eae7efba98135628d0c04af6e15495e
  MAJOR: cfgparse: make sure server names are unique within a backend

This was implemented as a post parsing check via
check_config_validity(). Now, this is performed directly during the
parsing of each new server instances. The main benefit is that it is a
much clearer operation.

Multiple checks are required : in _srv_parse_init() for standard server
and in _srv_parse_tmpl_init() for server-template. Note that the latter
check requires the following patch to ensure errors are properly
reported when duplicating a server-template instance.

  commit 467440a34f81c635ccb33d434328799b027cbf03
  MINOR: server: do not ignore errors during server-template init