Comment 3 for bug 1679617

The error in your log is:

Setting up shim-signed (1.27~16.10.1+0.9+1474479173.6c180c6-1ubuntu1) ...
Installing for x86_64-efi platform.
Installation finished. No error reported.
Running in non-interactive mode, doing nothing.
dpkg: error processing package shim-signed (--configure):
 subprocess installed post-installation script returned error exit status 1

This indicates that the shim package detected dkms modules present on your system, and that you have SecureBoot enabled, and therefore SecureBoot must be administratively disabled in order for you to continue booting.

And the prompt failed to be displayed, which made it impossible to configure this for you.

However, this should already have been the policy in place prior to your upgrade, so I'm not sure why you were prompted again. Could you please send the output of the following commands:
$ cat /proc/sys/kernel/moksbstate_disabled
$ od -tx1 /sys/firmware/efi/efivars/SecureBoot-8be4df61-93ca-11d2-aa0d-00e098032b8c
$ od -tx1 /sys/firmware/efi/efivars/MokSBStateRT-605dab50-e046-4300-abb6-3dd810dd8b23