This reverts commit ea6632c0.

This reverts commit 4359f5fd.

This reverts commit 7b7be65d.

This reverts commit 5f6d916f.

This reverts commit 6dca5a56.

This reverts commit 1132be27.

This reverts commit e406a26e.

A goal is that I'll be doing less sysadmin myself and so far, nobody else on
the sysadmin team is excited by the cloud option.

According to our data, our ISO builds are not slower recently than they were
before we switched to Vagrant, go figure. But we've lost the data from the
months immediately before the switch, so it's hard to tell whether I'm comparing
apples and oranges or what. Also, I guess we probably optimized other stuff
which compensates the nested virtualization overhead. Now it's too late to
measure the difference between the old & new setups when doing the exact same
job, so let's just give up.

 - Update the problem statement with more recent usage+performance data and to
   match the fact we've already deployed the reproducible builds CI changes we
   wanted.

 - Mention upcoming needs for non-CI services.

 - Entirely revamp the cloud section to be based on a hypothesis that can
   possibly work, and discuss some of the potentially hard problems.