DOCFIX-138: S8b -- centralize KEYSTONE_VIP default into lib-net.sh (single source of truth) ...

The keystone endpoint literal 10.12.4.50 was the default in 6 scripts (3 forms); now
all reference lib-net.sh KEYSTONE_VIP_DEFAULT (hard-rule #3). Sourced lib-net where
absent (verified source-safe). Each stays env-overridable. Resolve-checked; gauntlet
39/39, lint 0 fail (L7 re-recorded). S8 fully done (S8a+S8b); S8c won't-do.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

New Phase Scripts