Fixes the usage of PowerVMFileTransferFailed class

If it fails in the process of "Calculate file size in multiples of 512
bytes", the exception.PowerVMFileTransferFailed message is illegal.
"KeyError: u'file_path'" is occurs when there is no argument.

Change-Id: I15a7467bbc103f683d82949dc0892210cd63c4b6
Closes-Bug: #1223198
Merge "Fixes the usage of PowerVMFileTransferFailed class"