Make sure that the images are created with a non volatile root by default and
the vm are created with a volatile root by default. Break the --volatile
option into --volatile-image and --persistent-vm options.
* guix/scripts/system.scm (perform-action): Turn volatile? argument into
volatile-vm-root?.
(show-help): Introduce --volatile-image and --persistent-vm options instead of
--volatile.
(%default-options): Adapt it.
(%options): Handle those options.
(process-action): Honor them.
* doc/guix.texi (Invoking guix system): Adapt it accordingly.
2d12ec724e