vmm: Encompass guest payload configuration in PayloadConfig

Introduce a new top level member of VmConfig called PayloadConfig that
(currently) encompasses the kernel, commandline and initramfs for the
guest to use.

In future this can be extended for firmware use. The existing
"--kernel", "--cmdline" and "initramfs" CLI parameters now fill the
PayloadConfig.

Any config supplied which uses the now deprecated config members have
those members mapped to the new version with a warning.

See: #4445

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vmm/src/lib.rs

@@ -1968,8 +1968,8 @@ const DEVICE_MANAGER_SNAPSHOT_ID: &str = "device-manager";
 mod unit_tests {
     use super::*;
     use config::{
-        CmdlineConfig, ConsoleConfig, ConsoleOutputMode, CpusConfig, HotplugMethod, KernelConfig,
-        MemoryConfig, RngConfig, VmConfig,
+        CmdlineConfig, ConsoleConfig, ConsoleOutputMode, CpusConfig, HotplugMethod, MemoryConfig,
+        PayloadConfig, RngConfig, VmConfig,
     };
 
     fn create_dummy_vmm() -> Vmm {
@@ -2010,13 +2010,15 @@ mod unit_tests {
                 prefault: false,
                 zones: None,
             },
-            kernel: Some(KernelConfig {
-                path: PathBuf::from("/path/to/kernel"),
-            }),
-            initramfs: None,
+            kernel: None,
             cmdline: CmdlineConfig {
-                args: String::from(""),
+                args: String::default(),
             },
+            initramfs: None,
+            payload: Some(PayloadConfig {
+                kernel: Some(PathBuf::from("/path/to/kernel")),
+                ..Default::default()
+            }),
             disks: None,
             net: None,
             rng: RngConfig {