sanlock: improve repeated ballots in paxos_acquire
    
    The paxos implementation was inefficient in advancing the mbal
    between successive ballots.  If the local mbal was much less
    than the mbal used by other hosts, the local mbal was increased
    by just num_hosts repeatedly until it reached the other mbal.
    Now we advance the local mbal directly to the base value last
    seen from other hosts.
    
    Original suggestion/patch and final testing from 张伟.