xenapi: send chunk terminator on subprocess exc

During chunk upload if a subprocess exception is thrown, a malformed
chunk upload occurs.

This patch adds logging for subprocess exceptions and sends the
terminator even in the event of a subprocess exception. The incomplete
file upload will then be cleaned up by the client.

Change-Id: I559f201430bcd4c36d669c7772a10bfe3cd54d41
Closes-Bug: 1365637
Merge "xenapi: send chunk terminator on subprocess exc"