Description of problem:
As far as I can tell, dnf seems to delete or ignore all the rpms
it downloaded during a failed "dnf update" invocation. Ie next time
one runs "dnf update" it starts downloading all the files again. :-(

Version-Release number of selected component (if applicable):
dnf-1.0.1-2.fc22

How reproducible:
100%

Steps to Reproduce:
1. run "dnf update" and it fails due to some mirror being down
2. run "dnf update" again

Actual results:
1. various rpms/drpms get downloaded until fail due to missing rpm
from down server.
2. dnf downloads all the rpms/drpms (and fails again)

Expected results:
2. dnf should cache the rpms it already downloaded or not ignore them.

Additional info:
Yum did this correctly.