update-initramfs fails with cp: cannot create regular file '/cdrom/casper/initrd.gz.new': No such file or directory

[Newton Firefly]

failure during update and seem to have led to a complete system crash before or was from after a complete system crash which also had failures during update. The relevant dpkg terminal log says:

```
Setting up initramfs-tools (0.122ubuntu8.1) ...
update-initramfs: deferring update (trigger activated)
cp: cannot create regular file '/cdrom/casper/initrd.gz.new': No such file or directory
dpkg: error processing package initramfs-tools (--configure):
 subprocess installed post-installation script returned error exit status 1
```

ProblemType: Package
DistroRelease: Ubuntu 16.04
Package: initramfs-tools 0.122ubuntu8.1
ProcVersionSignature: Ubuntu 4.4.0-31.50-generic 4.4.13
Uname: Linux 4.4.0-31-generic i686
NonfreeKernelModules: wl
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: i386
Date: Wed Nov 2 03:11:24 2016
ErrorMessage: subprocess installed post-installation script returned error exit status 1
PackageArchitecture: all
RelatedPackageVersions:
 dpkg 1.18.4ubuntu1.1
 apt 1.2.12~ubuntu16.04.1
SourcePackage: initramfs-tools
Title: package initramfs-tools 0.122ubuntu8.1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.