DRILL-4258: Add threads, fragments, and queries system tables

[StevenMPhillips]

Here are the pojos that represent the data for the new system tables:

  public static class FragmentInfo {
    public String hostname;
    public String queryId;
    public int majorFragmentId;
    public int minorFragmentId;
    public Long memoryUsage;
    /**
     * The maximum number of input records across all Operators in fragment
     */
    public Long rowsProcessed;
    public Timestamp startTime;
  }

  public static class ThreadSummary {
    /**
     * The Drillbit hostname
     */
    public String hostname;

    /**
     * The Drillbit user port
     */
    public long user_port;
    public String threadName;
    public long threadId;
    public boolean inNative;
    public boolean suspended;
    public String threadState;
    /**
     * Thread cpu time during last second. Between 0 and 100
     */
    public Integer cpuTime;
    /**
     * Thread user cpu time during last second. Between 0 and 100
     */
    public Integer userTime;
    public String stackTrace;
  }

  public static class QueryInfo {
    /**
     * The host where foreman is running
     */
    public String foreman;
    /**
     * User who submitted query
     */
    public String user;
    public String queryId;
    /**
     * Query sql string
     */
    public String query;
    public Timestamp startTime;
  }

I did not include data in the query table which can be obtained from the fragments table and doing a join on the queryId.

[sudheeshkatkam]

There is a thread (WorkManager.StatusThread) that does periodic tasks (currently updates fragment statuses), how about we add this as another task?