Description of problem:
1. the default mirrorlist are not correct
2. after download the installer images and packages, error occured 

Version-Release number of selected component (if applicable):


How reproducible:
100%

Steps to Reproduce:
1. modify baseurl and installurl as below
   baseurl=http://download.fedoraproject.org/pub/fedora/linux/development/16/x86_64/os/
   installurl=http://dl.fedoraproject.org/pub/alt/stage/16-Alpha.TC1/Fedora/x86_64/os
2.run preupgrade - /path/to/releases.txt
3.
  
Actual results:
after everything is downloaded, 'Reboot Now' button appear. error message are given as below:

loaded plugins: blacklist, langpacks, whiteout
No plugin match for: rpm-warm-cache
No plugin match for: remove-with-leaves
No plugin match for: auto-update-debuginfo
preupgrade-main (baseurl)
  url: http://download.englab.nay.redhat.com/pub/fedora/linux/development/16/x86_64/os/
  now: http://download.englab.nay.redhat.com/pub/fedora/linux/development/16/x86_64/os/
preupgrade (baseurl)
  url: http://dl.fedoraproject.org/pub/alt/stage/16-Alpha.TC1/Fedora/x86_64/os/
  now: http://dl.fedoraproject.org/pub/alt/stage/16-Alpha.TC1/Fedora/x86_64/os/
unknown metadata being downloaded: MEMORY
Fetched treeinfo from http://dl.fedoraproject.org/pub/alt/stage/16-Alpha.TC1/Fedora/x86_64/os//.treeinfo
treeinfo timestamp: Mon Aug  1 17:54:37 2011
/boot/upgrade/vmlinuz checksum OK
/boot/upgrade/initrd.img checksum OK
Downloading 0.0bytes
Upgrade requires 500.0MB
Available disk space for /usr: 2.3GB
Kernel requires 26.0MB
Available disk space for /boot: 280.5MB
Traceback (most recent call last):
  File "/usr/share/preupgrade/preupgrade-gtk.py", line 259, in on_assistant_apply
    self._do_main()
  File "/usr/share/preupgrade/preupgrade-gtk.py", line 278, in _do_main
    self.main_preupgrade()
  File "/usr/share/preupgrade/preupgrade-gtk.py", line 576, in main_preupgrade
    comps = self.pu.instrepo.retrieveMD("group")
  File "/usr/lib/python2.7/site-packages/yum/yumRepo.py", line 1551, in retrieveMD
    return self._retrieveMD(mdtype)
  File "/usr/lib/python2.7/site-packages/yum/yumRepo.py", line 1559, in _retrieveMD
    thisdata = self.repoXML.getData(mdtype)
  File "/usr/lib/python2.7/site-packages/yum/yumRepo.py", line 1454, in <lambda>
    repoXML = property(fget=lambda self: self._getRepoXML(),
  File "/usr/lib/python2.7/site-packages/yum/yumRepo.py", line 1450, in _getRepoXML
    raise Errors.RepoError, msg
yum.Errors.RepoError: Cannot retrieve repository metadata (repomd.xml) for repository: preupgrade. Please verify its path and try again


Clicking the "Reboot Now" button, nothing is upgraded

Expected results:



Additional info: