Fix long lines in Ganeti.HTools.Types and add Make check

Since hlint doesn't check style issues but rather code only issues,
let's add a simple Makefile check for too-long lines, and fix the
single bad case we have currently.

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