Improve IPMI's _make_password_file method.

Take care of _make_password_file TODO:
Improve temp file handling for _make_password_file method.

Change-Id: I824dac3e66a72abac3fa498349fe4ebe0edbdc3d
Authored-by: Chris Krelle <nobodycam@gmail.com>
Merge "Improve IPMI's _make_password_file method."