In #12324 we made it so that plugins wait until the node drain is
complete, as we do for system jobs. But we neglected to mark the node
drain as complete once only plugins (or system jobs) remaining, which
means that the node drain is left in a draining state until the
`deadline` time expires. This was incorrectly documented as expected
behavior in #12324.
When a node is drained, system jobs are left until last so that
operators can rely on things like log shippers running even as their
applications are getting drained off. Include CSI plugins in this set
so that Controller plugins deployed as services can be handled as
gracefully as Node plugins that are running as system jobs.
