@Override
  public boolean isStopped() {
    return stopped;
  }
Generates a bulk assignment startup plan, attempting to reuse the existing assignment
information from META, but adjusting for the specified list of available/online servers
available for assignment.
<p>
Takes a map of all regions to their existing assignment from META. Also takes a list of online
servers for regions to be assigned to. Attempts to retain all assignment, so in some instances
initial assignment will not be completely balanced.
<p>
Any leftover regions without an existing server to be assigned to will be assigned randomly to
available servers.
@param regions regions and existing assignment from meta
@param servers available servers
@return map of servers and regions to be assigned to them, or emptyMap if no assignment is
        possible (ie. no servers)
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/BaseLoadBalancer.java