Because systemd did something obnoxious, the kernel retaliated in the
game of Core Wars by hiding all arguments before `--' from userspace.
So use `---' instead so that all the arguments remain visible.

This in some sense now applies to host installs a change we had
already made to Debian HVM guests.  See osstest#493b7395
  ts-debian-hvm-install: Use ---, and no longer duplicate $gconsole
and https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=762007
  Kernel command line handling change breaks d-i user-params functionality

This change is fine for all non-ancient versions of Debian, so I have
not made it conditional.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
---
 Osstest/TestSupport.pm | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Osstest/TestSupport.pm b/Osstest/TestSupport.pm
index f4e9414c..ff8103f2 100644
--- a/Osstest/TestSupport.pm
+++ b/Osstest/TestSupport.pm
@@ -2909,7 +2909,7 @@ label overwrite
 	menu label ^Overwrite
 	menu default
 	kernel $kern
-	append $dicmd initrd=$initrd -- $hocmd
+	append $dicmd initrd=$initrd --- $hocmd
 	ipappend $xopts{ipappend}
 	$dtbs
 default overwrite
@@ -2956,7 +2956,7 @@ sub setup_netboot_di_uefi ($$$$$;%) {
 set default=0
 set timeout=5
 menuentry 'overwrite' {
-  linux $kern $dicmd -- $hocmd
+  linux $kern $dicmd --- $hocmd
   initrd $initrd
 }
 END
-- 
2.20.1