KVM API says that KVM_RUN will return with -EINTR when a signal is
pending. However, if a vCPU is in KVM_MP_STATE_UNINITIALIZED, then
the return value is unconditionally -EAGAIN.

Copy over some code from vcpu_run(), so that the case of a pending
signal results in the expected return value.
Signed-off-by: NJan H. Schönherr <jschoenh@amazon.de>
Signed-off-by: NRadim Krčmář <rkrcmar@redhat.com>