multiple fixes to vcpu setup and memory allocation

xencall/examples/vcpu_context.rs

@@ -0,0 +1,12 @@
+use xencall::domctl::DomainControl;
+use xencall::{XenCall, XenCallError};
+
+fn main() -> Result<(), XenCallError> {
+    env_logger::init();
+
+    let call = XenCall::open()?;
+    let domctl: DomainControl = DomainControl::new(&call);
+    let context = domctl.get_vcpu_context(224, 0)?;
+    println!("{:?}", context);
+    Ok(())
+}