Comment 5 for bug 1594587

I was able to work around this stupidity by temporarily pulling the execute bit from setxkbmap as follows:

/var/cache/apt/archives⟫ which setxkbmap
/usr/bin/setxkbmap

/var/cache/apt/archives⟫ sudo chmod -x /usr/bin/setxkbmap

/var/cache/apt/archives⟫ sudo dpkg -i keyboard-configuration_1.108ubuntu15.2_all.deb
(Reading database ... 288650 files and directories currently installed.)
Preparing to unpack keyboard-configuration_1.108ubuntu15.2_all.deb ...
Unpacking keyboard-configuration (1.108ubuntu15.2) over (1.108ubuntu15.2) ...
Setting up keyboard-configuration (1.108ubuntu15.2) ...
update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults
update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults
update-initramfs: deferring update (trigger activated)
Processing triggers for systemd (229-4ubuntu8) ...
Processing triggers for man-db (2.7.5-1) ...
Processing triggers for initramfs-tools (0.122ubuntu8.1) ...
update-initramfs: Generating /boot/initrd.img-4.4.0-38-generic

/var/cache/apt/archives⟫ sudo chmod +x /usr/bin/setxkbmap

After doing that I was finally able to complete the rest of the upgrade.