Move Haskell constants to proper module

Move Haskell constants to proper module

Move Haskell constants from module 'Ganeti.HsConstants', which was a
transitional module part of the Haskell to Python constant generation
infrastructure, to module 'Ganeti.Constants'.

Signed-off-by: Jose A. Lopes <jabolopes@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>