Warnings instead of exceptions for ConfigurationManager if deployment type has not been determined

[DenisRumyantsev]

Description:
For some versions (e.g. 15), the Team Foundation Server cannot determine its own deployment type and return it to the agent (was not implemented yet). So the agent should write warnings to the diagnostic logs instead of errors when the deployment type determination is failed. However, if it is failed during the self-update process, the agent still should throw an exception, since:

• there will be no checksum validation if the OnPremises will be set by default — and no one will know about it until check the agent diagnostic logs (not secure)
• this can be skipped by setting the environment variable DISABLE_HASH_VALIDATION=true

ChangeLog:

• src/Microsoft.VisualStudio.Services.Agent/Util/ServerUtil.cs —

  • the DeploymentTypeNotDeterminedException and DeploymentTypeNotRecognizedException custom exceptions are added;
  • the TryIsDeploymentTypeHosted method implemented. When the agent cannot get the deployment type from the server, this method will write a warning using the Trace and return false, which means, that the deployment type is not Hosted.

• src/Agent.Listener/Configuration/ConfigurationManager.cs — the TryIsDeploymentTypeHosted method is used instead of the IsDeploymentTypeHosted method

• src/Agent.Listener/SelfUpdater.cs — added more info to the exception message

Related issue

[DenisRumyantsev]

Tested this pull request on the TFS 15. Changes work as expected. From now, in the pipeline agent diagnostic logs, during its configuration, the warning is displayed instead of the exception thrown.

[alexander-smolyakov]

LGTM, thanks!