scripts/kvm/vmxcap: Use Python 3 interpreter and add pseudo-main()

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200512103238.7078-5-philmd@redhat.com>

scripts/kvm/vmxcap

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python3
 #
 # tool for querying VMX capabilities
 #
@@ -275,5 +275,6 @@ controls = [
         ),
     ]
 
-for c in controls:
-    c.show()
+if __name__ == '__main__':
+    for c in controls:
+        c.show()