vmm: Introduce new --balloon parameter

This introduces a new way of defining the virtio-balloon device. Instead
of going through the --memory parameter, the idea is to consider balloon
as a standalone virtio device.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

src/main.rs

@@ -180,6 +180,13 @@ fn create_app<'a, 'b>(
                 .default_value(&default_rng)
                 .group("vm-config"),
         )
+        .arg(
+            Arg::with_name("balloon")
+                .long("balloon")
+                .help(config::BalloonConfig::SYNTAX)
+                .takes_value(true)
+                .group("vm-config"),
+        )
         .arg(
             Arg::with_name("fs")
                 .long("fs")
@@ -582,6 +589,7 @@ mod unit_tests {
                     src: PathBuf::from("/dev/urandom"),
                     iommu: false,
                 },
+                balloon: None,
                 fs: None,
                 pmem: None,
                 serial: ConsoleConfig {