An upgrade log records the upgrade activity. The upgrade log file
is named as the upgrade.log and is created in the domains
root where the upgrade is carried out.
After you have upgrade a domain, you can see a file whose name is in
the following format: upgradedTo<releasenumber>. For example, a domain that has been upgraded to 9.1 Update
1 will have a file called upgradeTo91 in its config folder.