cleanup windows version handling and hyperv enlightments

cleanup windows version handling and hyperv enlightments

This cleanup windows guest os version handling,
with normalizing ostype with numbers in a new windows_version sub.

if($ostype eq 'wxp' || $ostype eq 'w2k3' || $ostype eq 'w2k') {
      $winversion = 5;
} elsif($ostype eq 'w2k8' || $ostype eq 'wvista') {
      $winversion = 6;
} elsif ($ostype =~ m/^win(\d+)$/) {
      $winversion = $1;
}

so we can simply do test on windows version with lower or upper version

Hyperv enlightments configuration is centralized
in a new add_hyperv_enlighments sub.

Also disable hyperv with win < 8 + ovmf.

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>