software/kvm: fix wipe-disk-device-wrapper

Without a shebang, supervisord refuses to run the script with the
following error:

supervisor: couldn't exec /srv/slapgrid/slappart8/etc/prerm/slapos_wipe_device_disk: ENOEXEC
supervisor: child process was not spawned

This is a fixup of 0983f1ca

software/kvm/buildout.hash.cfg

@@ -19,7 +19,7 @@ md5sum = f2b0f1ed27148504f220e06eaceff935
 
 [template-kvm]
 filename = instance-kvm.cfg.jinja2
-md5sum = f902dd10cb052ac262a4a96b9362b3a3
+md5sum = 93cbee3403e7e23b4278143c32209ddc
 
 [template-kvm-cluster]
 filename = instance-kvm-cluster.cfg.jinja2.in

software/kvm/instance-kvm.cfg.jinja2

@@ -1177,6 +1177,7 @@ context =
 [wipe-disk-device-wrapper]
 recipe = slapos.recipe.template:jinja2
 template = inline:
+  #!/bin/sh
 {%- for disk_device in disk_device_path.split() %}
   dd if=/dev/zero of={{ disk_device }} bs=4096 count=500k
 {%- endfor %}