Enabling ACID transactions

In order to use ACID transactions in Hive-MR3, the user should initialize the database schema when running Metastore for the first time (e.g., by executing `hive/metastore-service.sh` with `--init-schema`). Then the user can enable ACID transcations by provide additional configuration settings for Metastore, HiveServer2, and HiveCLI. Here is an example of configuring Metastore for enabling ACID transactions: * set `hive.compactor.initiator.on` to true. * set `hive.compactor.worker.threads` to an integer greater than 0. Here is an example of configuring HiveServer2 or HiveCLI for enabling ACID transactions: * set `hive.support.concurrency` to true. * set `hive.enforce.bucketing` to true (which is unnecessary for Hive-MR3 based on Hive 2.x). * set `hive.exec.dynamic.partition.mode` to `nonstrict`. * set `hive.txn.manager` to `org.apache.hadoop.hive.ql.lockmgr.DbTxnManager`.