Fix the way we downgrade ftp mirrors, for hosts which give us both

# Please enter the commit message for your changes.
# (Comment lines starting with '#' will not be included)
# On branch master
# Changes to be committed:
#   (use "git reset HEAD^1 <file>..." to unstage)
#
#	modified:   plugins/fastestmirror/fastestmirror.py
#
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#	avahi-packages-server.py
#	csb-release-6-3.rhis.noarch.rpm
#	dircheck-remote.py
#	plugins/Avahi/
#	plugins/categories/
#	plugins/conf/
#	plugins/download-limit/
#	potential_conflict-james.py
#	potential_conflict.py
#	yum-debug-restore.py