SVM: add test for nested guest RIP corruption

This adds a unit test for SVM nested register corruption that happened when
L0 emulated an instruction and just before injecting a vmexit, and upon
vmexit the VMCB contained pre-emulation values of RAX, RIP and RSP.
This test detects RIP corruption when RIP is at the start of
the emulated instruction but the instruction was already executed.

The upstream commit that fixed this bug is b6162e82aef19fee9c32cb3fe9ac30d9116a8c73
  KVM: nSVM: Preserve registers modifications done before nested_svm_vmexit()

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20200622165533.145882-1-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>