BUG/MINOR: lua: don't expose internal proxies

Since internal proxies are now in the global proxy list, they are now
reachable from core.proxies, core.backends, core.frontends.

This patch fixes the issue by checking the PR_CAP_INT flag before
exposing them in lua, so the user can't have access to them.

This patch must be backported in 2.5.
1 file changed