hypervisor: introduce a new function

It returns an hypervisor object depending on which hypervisor is
configured.  Currently it only supports KVM.

Signed-off-by: Wei Liu <liuwe@microsoft.com>

hypervisor/src/lib.rs

@@ -44,3 +44,11 @@ pub use crate::hypervisor::{Hypervisor, HypervisorError};
 pub use cpu::{HypervisorCpuError, Vcpu, VmExit};
 pub use kvm::*;
 pub use vm::{DataMatch, HypervisorVmError, Vm};
+
+use std::sync::Arc;
+pub fn new() -> std::result::Result<Arc<dyn Hypervisor>, HypervisorError> {
+    #[cfg(feature = "kvm")]
+    let hv = kvm::KvmHypervisor::new()?;
+
+    Ok(Arc::new(hv))
+}