Fix generating empty cache on controller

[gmshake]

ZipExtractionInstaller.performInstallation() will invoke FilePath.installIfNecessaryFrom() to extract tar ball. When there is no connection to the binary_link and the filepath expected exists, no exception will be thrown thus it falls though to generate and send an emptly cache file to the master. Next rounds requests to install the same JDK tool will result in empty tool directory on slave nodes.

Fix that by skip creating empty tool directory on slave nodes.

Testing done

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[MarkEWaite]

Please provide a test that shows the failure before your change and does not show the failure after your change.

The expected.deleteRecursive(); that precedes the line you removed is intended to remove the directory expected and its chilldren then expected.mkdirs() recreates the directory expected.

[MarkEWaite]

I don't understand what you mean when you say:

When there is no connection to the binary_link and the filepath expected exists

I see no mention of binary_link in any of the code, either Jenkins core or in the plugin. Can you explain further?