Cancelling an upgrade reports wrong upgrade date

[Moshe Caspi]

Steps to reproduce:

1. Start an upgrade.
2. Cancel it after reading some information about the upgrade.
3. Next time, when a user wants to report a bug to Launchpad, the date of the upgrade of the user's current Ubuntu version that will be passed to Launchpad will be the date he activated steps 1 and 2 instead of the actual upgrade date which was much earlier.

For example: I upgrade to Xenial much earlier than this report:

UpgradeStatus: Upgraded to xenial on 2018-08-28 (54 days ago)

It looks like the date of an upgrade needs to be set when a user ends the procedure and not when he starts it.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: update-manager 1:16.04.14
ProcVersionSignature: Ubuntu 4.4.0-137.163-generic 4.4.144
Uname: Linux 4.4.0-137-generic i686
ApportVersion: 2.20.1-0ubuntu2.18
Aptdaemon:

Architecture: i386
CurrentDesktop: LXDE
Date: Sun Oct 21 13:21:25 2018
GsettingsChanges:
 b'com.ubuntu.update-manager' b'show-details' b'true'
 b'com.ubuntu.update-manager' b'window-height' b'741'
 b'com.ubuntu.update-manager' b'first-run' b'false'
 b'com.ubuntu.update-manager' b'window-width' b'1366'
 b'com.ubuntu.update-manager' b'launch-time' b'int64 1540045540'
InstallationDate: Installed on 2015-01-06 (1383 days ago)
InstallationMedia: Lubuntu 14.10 "Utopic Unicorn" - Release i386 (20141022.1)
PackageArchitecture: all
SourcePackage: update-manager
UpgradeStatus: Upgraded to xenial on 2018-08-28 (54 days ago)