With the new oslo-privsep library, there is now a
privsep-helper command that is used to escalate
privledges.
This command needs to be runnable by the nova user
via sudo without a password. The old rootwrap command
is still used as well, so for now we need to have
both.
Change-Id: I3bf334bf9498f67a1e91041d1d50870964e6141c