Instructs Spock to use
CleanupTestDirectoryExtension to clean up the test directory provided by a
TestDirectoryProvider. This is to work around the fact that using
a test directory provider as a TestRule causes spock to swallow any test failures and the test directory
is cleaned up even for failed tests.
CleanupTestDirectoryExtension on the other hand, registers
an interceptor and listener which cleans up the test directory only when the test passes.
The annotation needs to know which field is the
TestDirectoryProvider
to clean up. It defaults to "temporaryFolder", which is the field for AbstractIntegrationSpec. Other specs
can set it accordingly using "fieldName".