tests: centralize default CPU arguments in test infrastructure

Replace the hard-coded  .args(["--cpus", "boot=1"]) in the simple
launch integration test with a shared helper (default_cpus) from test
infrastructure.

Extend Guest with explicit CPU-related defaults (num_cpu, nested)
and add default_cpus_string() so CPU configuration is derived from
guest state instead of being duplicated at call sites.

This refactor improves consistency and makes CPU defaults easier to
maintain across integration tests.

Signed-off-by: Muminul Islam <muislam@microsoft.com>

cloud-hypervisor/tests/integration.rs

@@ -2545,7 +2545,7 @@ fn _test_simple_launch(guest: &Guest) {
     let event_path = temp_event_monitor_path(&guest.tmp_dir);
 
     let mut child = GuestCommand::new(guest)
-        .args(["--cpus", "boot=1"])
+        .default_cpus()
         .args(["--memory", "size=512M"])
         .default_kernel_cmdline()
         .default_disks()

test_infra/src/lib.rs

@@ -916,6 +916,8 @@ pub struct Guest {
     pub kernel_path: Option<String>,
     pub kernel_cmdline: Option<String>,
     pub console_type: Option<String>,
+    pub num_cpu: u32,
+    pub nested: bool,
 }
 
 // Return the next id that can be used for this guest. This is stored in a
@@ -985,6 +987,8 @@ impl Guest {
             kernel_path: None,
             kernel_cmdline: None,
             console_type: None,
+            num_cpu: 1u32,
+            nested: true,
         }
     }
 
@@ -1373,6 +1377,14 @@ impl Guest {
         }
         out_evt
     }
+
+    pub fn default_cpus_string(&self) -> String {
+        format!(
+            "boot={}{}",
+            self.num_cpu,
+            if self.nested { "" } else { ",nested=off" }
+        )
+    }
 }
 
 #[derive(Default)]
@@ -1555,6 +1567,10 @@ impl<'a> GuestCommand<'a> {
 
         self
     }
+
+    pub fn default_cpus(&mut self) -> &mut Self {
+        self.args(["--cpus", self.guest.default_cpus_string().as_str()])
+    }
 }
 
 /// Returns the absolute path into the workspaces target directory to locate the desired