Disable HBase System tables

[Stephen Jiang]

In disable table, we specifically check whether it is a META table; if a
table is a META table, we disallow the table disable.  However, I think
other system tables should have the same treatment (is it possible that a
namespace table is disable and the system is still functional without
issue?).

    if(tableName.equals(TableName.META_TABLE_NAME)) {

      throw new ConstraintException("Cannot disable catalog table");

    }
I want to extend the disable-not-allowed treatment to all system tables,
please let me know if you disagree.

Thanks
Stephen