jenkinks: jobs: bifrost: Fix order of builders

bifrost now has a bindep.txt file in the root of the repository
so we need to use 'zuul-git-prep-upper-constraints' before the
'install-distro-packages' one in order for our 'bindep.txt' file to
be used. This fixes the following problem on jobs where the bindep.txt
is not being used:

2017-06-22 16:05:46.680832 | + /usr/local/jenkins/slave_scripts/install-distro-packages.sh
2017-06-22 16:05:46.682662 | + export BINDEP=/usr/bindep-env/bin/bindep
2017-06-22 16:05:46.682699 | + BINDEP=/usr/bindep-env/bin/bindep
2017-06-22 16:05:46.682713 | + YUM=yum
2017-06-22 16:05:46.682723 | + is_fedora
2017-06-22 16:05:46.682738 | + '[' -f /usr/bin/yum ']'
2017-06-22 16:05:46.683312 | + grep -q -e Fedora
2017-06-22 16:05:46.683544 | + cat /etc/centos-release /etc/os-release /etc/redhat-release /etc/system-release
2017-06-22 16:05:46.684551 | + '[' -n '' ']'
2017-06-22 16:05:46.684587 | + '[' -e bindep.txt ']'
2017-06-22 16:05:46.684609 | + '[' -e other-requirements.txt ']'
2017-06-22 16:05:46.684638 | + export PACKAGES=/usr/local/jenkins/common_data/bindep-fallback.txt
2017-06-22 16:05:46.684686 | + PACKAGES=/usr/local/jenkins/common_data/bindep-fallback.txt

Change-Id: I5c780240f495f28f6cb325095c1a634c87eb06f8

jenkins/jobs/bifrost.yaml

@@ -7,10 +7,10 @@
           timeout: 60
 
     builders:
-      - install-distro-packages
       - link-logs
       - net-info
       - zuul-git-prep-upper-constraints
+      - install-distro-packages
       - shell: |
           #!/bin/bash -eux
           cd $WORKSPACE