static int calcPriority(int priority, TableName tableName) {
    if (priority != HConstants.PRIORITY_UNSET) {
      return priority;
    } else {
      return getPriority(tableName);
    }
  }
Select the priority for the rpc call.
<p/>
The rules are:
<ol>
<li>If user set a priority explicitly, then just use it.</li>
<li>For system table, use {@link HConstants#SYSTEMTABLE_QOS}.</li>
<li>For other tables, use {@link HConstants#NORMAL_QOS}.</li>
</ol>
@param priority  the priority set by user, can be {@link HConstants#PRIORITY_UNSET}.
@param tableName the table we operate on
hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionUtils.java