x86: Add support for running a nested guest multiple times in one test

KUT has a limit of only being able to run one nested guest per vmx test.
This is limiting and not necessary.  Add support for allowing a test to
run guest code multiple times.

Signed-off-by: Aaron Lewis <aaronlewis@google.com>
Message-Id: <20220125203127.1161838-3-aaronlewis@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>