Further fixes for new-style exception handling

Commit 30d25dd8 moved the htools code to new-style exception handling,
but the hconfd code hasn't been, which fails when compiling on newer
GHC versions.

This patch does the rest of the move; however, the situation is not
very nice, we should have a better way to handle this (introduce
catchIO? or something like that).

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>