Move src/Ganeti/HTools/Program.hs to Program/Main.hs

This removes one more tab conflict; this is the last module in our
code where we have both x.hs and x/.

Furthermore, we collapse all actual code into the new Main.hs module,
leaving the htools.hs basically empty (will allow better testing in
the future).

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