This changes the CLI specification for disks, as it needs to be able to
be repeated.
```
linuxkit run qemu -disk name,size=1G,format=qcow2 ...
```
Options may be omitted.
Currently other local backends may not support multiple disks, but this
can be added in future. Code for cloud backends has not changed as the
disk support is specific to the platform.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
- '-disk-size' is now defaults to MB (but can be GB when appending 'G')
- The disk will be created if it doesn't exist (didn't happen in qemu)
Update the documentation.
Signed-off-by: Rolf Neugebauer <rolf.neugebauer@docker.com>
