kvm-unit-tests: VMX: Test cases for nested EPT

Some test cases for nested EPT features, including:
1. EPT basic framework tests: read, write and remap.
2. EPT misconfigurations test cases: page permission mieconfiguration
and memory type misconfiguration
3. EPT violations test cases: page permission violation and paging
structure violation

Signed-off-by: Arthur Chunqi Li <yzt356@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>