Fixed Issues in Apache Kudu

Review the list of Kudu issues that are resolved in Cloudera Runtime 7.2.2.

KUDU-2373: maintenance-manager-num-threads=0 causes CHECK fail during server startup

Setting the gflag maintenance_manager_num_threads to 0 causes a failure during server setup. A flag validator was added to prevent this.

KUDU-3184: Fix GetFQDN() when canonical name returns null

If FQDN did not have domain name (ex .local), canonical name was not assigned and FQDN returned null.