Test what happens when writing data to an external data file, where the
write requires an L2 entry to be allocated, but the data write fails.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200225143130.111267-4-mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>