disks should synchronize with fstab

When gnome-disk-utility formats a disk it assigns a new UUID.
UUID is the preferred way to identify disks in fstab.
Problem is that gnome-disk-utility does *not* update fstab.
As a consequence the system will not boot & newbies will be stumped. (I was for two days).
Therefore gnome-disk-utility must check fstab and if appropriate
not assign a new UID
or
update fstab
or
alert the user to update fstab.

And, yes, this is a bug, albeit a bug in the design, but still a bug.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: gnome-disk-utility 3.18.3.1-1ubuntu1
ProcVersionSignature: Ubuntu 4.10.0-42.46~16.04.1-generic 4.10.17
Uname: Linux 4.10.0-42-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.14
Architecture: amd64
CurrentDesktop: Unity
Date: Sun Dec 17 13:45:45 2017
ExecutablePath: /usr/bin/gnome-disks
InstallationDate: Installed on 2017-12-13 (3 days ago)
InstallationMedia: Ubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
SourcePackage: gnome-disk-utility
UpgradeStatus: No upgrade log present (probably fresh install)