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: I6347dec4cfda61bed0960159e8a3402fcffa296b
Merge "Remove junk file when ftp transfer failure" into stable/grizzly