http proxy rewrite map should catch user group lookup failure

Currently the rewrite map look for gpfs5 group. when lookup failed, it fall back to gpfs4 which is not desired.

• HTTP Router is less sensitive to lookup failures because it goes directly to LDAP - if LDAP lookup fails, Apache likely returns a 500-level error.

  In the http rewrite map we have three situations currently:

  • lookup and route user to gpfs4
  • lookup and route user to gpfs5
  • lookup failed and send to gpfs4( default)

This would require updating all users on GPFS4 filesystem to be explicitly marked as GPFS4 group members, and updating the logic in http routers to handle lookup failures more deterministically.