When the context is closed, FileWritingMessageHandler is stopped and
it closes its output files. However, it appears to do so in a manner
which means that they may be closed after the call to close the
context is completed. This causes problems on Windows as files that
are still open cannot be deleted.

This commit adds a workaround to SampleIntegrationApplicationTests
so that it makes up to 10 attempts each 0.5s apart to clean up the
input and output directories.