Today, because we don't wait for execvpe to finish to continue onwards,
it's possible that if you did an exec quick enough after starting an
init process for a container, that you could join the init processes
namespaces before pivot_root has taken place which is quite fun. Let's
wait for exec to finish (or an error to occur) to prevent this.
Systemd loves to move the root cgroups processes to one it created named
/init.scope and then write the root cgs subtree_control file. Because of
this we can't just add exec processes to the cg we made for the
container anymore as we'll get EBUSY. We should follow where the init
processes cg is actually at (/proc/pid/cgroup) and add it there.
Reverts f9198d6ff7
We can explore better approaches to some of the targets, but for now
lets revert as it interferes with being able to build even if we have
local changes.
J Logan