engine-iso-uploader - notify the user for started upload process

In upload_to_storage_domain notify the user that the upload process
has started.
Log also the starting of every upload, not only the completion.

In upload_to_storage_domain fixed redefinition of built-in 'file'

Change-Id: Id45632a662b12d8681dc99b2924105601a0e0d36
Bug-Url: https://bugzilla.redhat.com/785670
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>