Update add machine command to create containers
The add machine command accepts additional command line
arguments to specify a container to create. The container
can be on a new machine or an existing instance. Container
constraints are also supported eg create a container with
2G memory. The state is updated with the new machine document
but the machine watcher ignores the machine since there's no
code to provision containers yet.
examples:
juju add-machine /lxc
juju add-machine --constraints mem=4G /lxc
juju add-machine 1/lxc
R=mue, fwereade, thumper
CC=
https://codereview.appspot.com/9886045