Hello,

Here are two patches that should fix the "Installer fails when
restarted" issue.

For memory, the issue is caused by the store overlay created at
cow-store service start that I was unable to remove. Failing to remove
this overlay, caused the target device to be seen as busy by the kernel
and made further umount calls to fail[1].

I also fixed the "installation failed dialog". There are now two
options:
* "Resume": let the user resume the installation from any step (from the
installation menu)
* "Retry": restart the installer process.

WDYT?

Thanks,

Mathieu