Enabling validation of checksum for online agent update for ADO OnPrem

[denis-tikhomirov]

Enabled validation of checksum for online agent update for ADO OnPrem. Previously the validation was actual for Hosted ADO versions.
Validation of checksum is left as disabled for offline agent update (https://docs.microsoft.com/en-us/azure/devops/pipelines/agents/agents?view=azure-devops-2019&tabs=browser#can-i-update-my-v2-agents-that-are-part-of-an-azure-devops-server-pool).

Changes are tested by following cases:

• ADO On-Premises:
  • Update by button "Update all agents" with enabled network and without package in %ProgramData%\Microsoft\Azure DevOps\Agents - Checksum was successful
  • Update by start new task on agent with enabled network and without package in %ProgramData%\Microsoft\Azure DevOps\Agents - Checksum was successful
  • Update by button "Update all agents" with enabled network and with package in %ProgramData%\Microsoft\Azure DevOps\Agents - Checksum was skipped
  • Update by start new task on agent with enabled network and with package in %ProgramData%\Microsoft\Azure DevOps\Agents - Checksum was skipped
  • Update by button "Update all agents" with disabled network and with package in %ProgramData%\Microsoft\Azure DevOps\Agents - Checksum was skipped
  • Update by start new task on agent with disabled network and with package in %ProgramData%\Microsoft\Azure DevOps\Agents - Checksum was skipped
• Hosted ADO:
  • Update by button "Update all agents" with enabled network and without package in %ProgramData%\Microsoft\Azure DevOps\Agents - Checksum was successful
  • Update by start new task on agent with enabled network and without package in %ProgramData%\Microsoft\Azure DevOps\Agents - Checksum was successful

[anatolybolshakov]

LGTM, thanks!