[QA] interrupted upload produces a currupt file without notice

[jnweiger]

Seen with files_primary_s3 1.4.0 rc.2 on core 10.11.0

• Start upload of a large file (several GB) via e.g.
  curl --user $user:$pass -o /dev/stderr -T $file https://$servername/remote.php/dav/files/$user/
• Interrupt the upload by pressing CTRL-C at the shell.
• The $file appears in owncloud. But it is short.

Expected behaviour:

• incomplete uploads do not make it into the filesystem. The part files are discarded.
• (or) the $file is created as e.g. $file.partial - so that the user sees, that something is wrong.

[jnweiger]

As per feedback from @GeraldLeikam we can assume this behaviour is specific to s3 storage. with normal primary storage incomplete uploads do not appear.