Add event injection test

Add various event injection test. Those tests use testdev to unmap
pages from shadow pages/ept tables which make it possible to test
rare scenarios.

[avi: my compiler didn't like "foo"R"bar", added spaces]

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>