flash-kernel is not triggered on RISC-V

The live installer image fails to install a bootable system on the SiFive Unmatched board because the device tree that the kernel is using is the u-boot one, not the one in the kernel. This is because flash-kernel is not triggered during the installation process since a recent patch prevented it to run in a chroot.

But this patch also introduced a new environment variable to circumvent this: curtin should use this variable when installing the kernel so that flash-kernel is correctly triggered and installs the dtbs at the right place for GRUB.

I tested the following patch locally and it works fine:

diff --git a/curtin/commands/curthooks.py b/curtin/commands/curthooks.py
index 40011660..efb72ce4 100644
--- a/curtin/commands/curthooks.py
+++ b/curtin/commands/curthooks.py
@@ -373,7 +373,10 @@ def install_kernel(cfg, target):
         distro.install_packages(fk_packages.split(), target=target)

     if kernel_package:
- distro.install_packages([kernel_package], target=target)
+ env = os.environ.copy()
+ env["FK_FORCE"] = "yes"
+ env["FK_FORCE_CONTAINER"] = "yes"
+ distro.install_packages([kernel_package], target=target, env=env)
         return

     # uname[2] is kernel name (ie: 3.16.0-7-generic)
--
2.34.1