Change self.login() to self.wait_for_login() to allow call vm.get_cpu_count() before guest ssh running

Otherwise, calling would fail.

Signed-off-by: Xiaoqing Wei <xwei@redhat.com>
update the kvm_vm to support maxcpus sub option

maxcpus is a sub-option of -smp, so need a Regrex to match

Signed-off-by: Xiaoqing Wei <xwei@redhat.com>