test_infra: Allow to not print commandline when spawning guest

keep it as default to print out commandline when spawning guest in favor
of integration tests for debugging purpose, while allowing to disable
it when needed (e.g. for performance tests).

Signed-off-by: Bo Chen <chen.bo@intel.com>

test_infra/src/lib.rs

@@ -1185,6 +1185,7 @@ pub struct GuestCommand<'a> {
     command: Command,
     guest: &'a Guest,
     capture_output: bool,
+    print_cmd: bool,
 }
 
 impl<'a> GuestCommand<'a> {
@@ -1197,6 +1198,7 @@ impl<'a> GuestCommand<'a> {
             command: Command::new(clh_command(binary_name)),
             guest,
             capture_output: false,
+            print_cmd: true,
         }
     }
 
@@ -1205,13 +1207,20 @@ impl<'a> GuestCommand<'a> {
         self
     }
 
+    pub fn set_print_cmd(&mut self, print_cmd: bool) -> &mut Self {
+        self.print_cmd = print_cmd;
+        self
+    }
+
     pub fn spawn(&mut self) -> io::Result<Child> {
-        println!(
-            "\n\n==== Start cloud-hypervisor command-line ====\n\n\
-                 {:?}\n\
-                 \n==== End cloud-hypervisor command-line ====\n\n",
-            self.command
-        );
+        if self.print_cmd {
+            println!(
+                "\n\n==== Start cloud-hypervisor command-line ====\n\n\
+                     {:?}\n\
+                     \n==== End cloud-hypervisor command-line ====\n\n",
+                self.command
+            );
+        }
 
         if self.capture_output {
             let child = self