Remove junk file when ftp transfer failure

During spawn with powervm driver, the image transfer to the IVM host
may fail in some conditions, eg. IVM host doesn't have enough disk
space. It leaves the junk file in IVM host, and this will disturb
next spawn after resolving environment issue, need clean it.

Fixes bug #1188884

Change-Id: I7b8d719995c2702c89cf55cef5f34bde9d01c1b9
Merge "Remove junk file when ftp transfer failure"