Run environment.d hook for manifests earlier

15-pip-manifests depends on the variables defined by the manifests
element, so we need to run this one earlier. I would have thought things
were alpha sorted after the numerical sort...but I just ran into this,
so apparently not.

Change-Id: Ifedf544222b5a8eb7630efda609eb6a5b9629de3
Merge "Run environment.d hook for manifests earlier"