journal: move the gist of server_fix_perms to acl-util.[hc]

journal: move the gist of server_fix_perms to acl-util.[hc]

Most of the function is moved to acl-util.c to make it possible to
add tests in subsequent commit.

Setting of the mode in server_fix_perms is removed:
- we either just created the file ourselves, and the permission be better right,
- or the file was already there, and we should not modify the permissions.

server_fix_perms is renamed to server_fix_acls to better reflect new
meaning, and made static because it is only used in one file.