confd: add support for upgrading container images

This patch adds a new CLI command 'container upgrade foo', where 'foo'
is the name of the container.  If more than one container use the same
image, multiple upgrades must be done because a container runs not on
the 'image:tag' but on the hash of the 'image:tag' it was created from.

Rename "done" queue to "active", since we want to recreate an active
container after fetching an updated base image.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

package/execd/execd.conf

@@ -1,2 +1,2 @@
 service log:prio:local1.err,tag:container \
-	[2345] execd /run/containers/queue /var/lib/containers/done -- Container job runner
+	[2345] execd /run/containers/queue /var/lib/containers/active -- Container job runner

package/execd/tmpfiles.conf

@@ -1,5 +1,5 @@
 d  /run/containers/args		0700 - -
-d  /var/lib/containers/done	0700 - -
+d  /var/lib/containers/active	0700 - -
 d  /run/containers/inbox	0700 - -
 d  /run/containers/queue	0700 - -
 d  /run/cni			0755 - -