Fix error during cluster initialization due to hv_kvm

Commit 141d1489 was a bit too enthusiastic. The three parameters added to
the list of parameters to be checked default to a value not evaluating
to false, leading to a failure on cluster initialization.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>