Detect big scheduling pauses

Add poll timer scheduler to be called 3 times per token timeout.
If poll timer was not called for more then 0.8 * token timeout, it means
corosync process was not scheduled and ether token_timeout should be
increased or load should be reduced (useful for VM, where host is
overcommitted so VM is not scheduled as expected).

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Fabio M. Di Nitto <fdinitto@redhat.com>