Added a few test helpers for creating disk resources.
Added a few test helpers for creating disk resources.

Review: https://reviews.apache.org/r/63257

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