Run domtool as hcoop.daemon instead of hcoop

Run domtool as hcoop.daemon instead of hcoop

Previous releases inadvertently took advantage of a weakness in
domtool's afs acls to access the hcoop key when interacting with
domtool. Now that it has been fixed, a dummy domtool user
`hcoop.daemon' with no permissions exists so that it can authenticate
to domtool and perform the simple queries required by the portal.

We still have to set DOMTOOL_USER internally because suexec scrubs the
environment and using mod_env to set it does not work.