Multiple late_command entries in preseed

[Matt Hart <matthew.hart@linaro.org>]

Hi all,
TL;DR Can d-i support multiple late_command entries in a preseed?

Long version:
I'm adding support for testing automated installers into LAVA
(https://validation.linaro.org/static/docs/#what-is-lava) which lets
testers provide a kernel, ramdisk and preseed file which LAVA boots
on a device and follows the install through.

I need to use a late_command to copy some files into the installed target
so we can test the installed system when it boots. But I also have to
support users providing a preseed file that already has a late_command.

This makes for some awkward parsing of backslashes and semicolons
where I have to work out how to add an extra command at the end of the
string they have already defined.
As you can imagine, appending another late_command to the file would
be considerably easier. Or late_command2, late_command3 etc.

Maybe there's an easier way of doing this and I've missed something?

Thanks,
Matt