esxi import: add "longhorn" to possible Windows Server 2008 OS types

While we detected "winLonghorn" already as w2k8, it seems that some
ESXi versions also use "longhorn" here.

Add that to our known Windows OS type mapping, so that it gets
correctly mapped to our w2k8 type, which affects the selected
hardware.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

src/PVE/Storage/ESXiPlugin.pm

@@ -875,6 +875,7 @@ sub is_windows {
 
 my %guest_types_windows = (
     'dos'                   => 'other',
+    'longhorn'              => 'w2k8',
     'winNetBusiness'        => 'w2k3',
     'windows9'              => 'win10',
     'windows9-64'           => 'win10',