Fixed a bug where quota headroom is under-calculated.
Fixed a bug where quota headroom is under-calculated.

When calculating the quota headroom, we failed to consider
ancestor's reservation allocated to the child. This leads
to under-calculation of available headroom and excessive
resources being set aside for headroom. See MESOS-8604.

This patches fixes this issue by counting ancestor's reservation
allocated to the child as allocated-reservation even though
the child itself has no reservation.

Review: https://reviews.apache.org/r/65806/

asamerh4/mesos,andschwa/mesos,asamerh4/mesos,gsantovena/mesos,chhsia0/mesos,asamerh4/mesos,kaysoky/mesos,reneploetz/mesos,andschwa/mesos,jpeach/mesos,chhsia0/mesos,kaysoky/mesos,gsantovena/mesos,abudnik/mesos,andschwa/mesos,gsantovena/mesos,reneploetz/mesos,kaysoky/mesos,Gilbert88/mesos,andschwa/mesos,abudnik/mesos,jpeach/mesos,chhsia0/mesos,chhsia0/mesos,reneploetz/mesos,dforsyth/mesos,reneploetz/mesos,kaysoky/mesos,Gilbert88/mesos,dforsyth/mesos,Gilbert88/mesos,reneploetz/mesos,gsantovena/mesos,asamerh4/mesos,chhsia0/mesos,abudnik/mesos,asamerh4/mesos,kaysoky/mesos,gsantovena/mesos,dforsyth/mesos,abudnik/mesos,chhsia0/mesos,dforsyth/mesos,andschwa/mesos,dforsyth/mesos,jpeach/mesos,jpeach/mesos,chhsia0/mesos,jpeach/mesos,reneploetz/mesos,dforsyth/mesos,abudnik/mesos,asamerh4/mesos,Gilbert88/mesos,dforsyth/mesos,gsantovena/mesos,andschwa/mesos,Gilbert88/mesos,jpeach/mesos,andschwa/mesos,kaysoky/mesos,abudnik/mesos,kaysoky/mesos,Gilbert88/mesos,jpeach/mesos,Gilbert88/mesos,reneploetz/mesos,gsantovena/mesos,abudnik/mesos,asamerh4/mesos