local-mirrors.conf: add mirror for sourceforge and re-tries for wget

The downloads.sourceforge.net is unstable sometimes so the do_fetch
may fail for some packages, do the following to avoid that:

- add two mirror url so it will try to download from mirror url
  when downloads.sourceforge.net is unavailable.

- re-define the FETCHCMD_wget to add more re-tries (2 -> 5) and
  longer timeout (30 -> 60).

Issue-ID: INF-211
Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Change-Id: Ic6c9868fc1f2c470fe53a76e54a022dfc41c4589