The hardcoded URL seems to be broken and 404 error was not
checked. Now the mirror is selected from mirrorlist (instead of
hardcoding to funet.fi) and fetch errors are checked.

Also added a retry loop (with 3 tries) to find a working mirror, since
some of the mirrors are not OK.
Signed-off-by: Tuomas Suutari <tuomas.suutari@gmail.com>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>