remove HiveMain check for HADOOP_HOME

HiveMain is checking for HADOOP_HOME env to be defined.

In Hadoop 0.23 HADOOP_HOME does not exist anymore.

This check was in place because Hive requires the location of the 'hadoop' script and the Hadoop conf/ directory and uses HADOOP_HOME to determine its value.

If HADOOP_HOME is not defined Hive fails unless the following properties are defined in the hive-site.xml

<property>
<name>hadoop.bin.path</name>
<value>[PATH_TO_HADOOP_ROOT]/bin/hadoop</value>
</property>

<property>
<name>hadoop.config.dir</name>
<value>[PATH_TO_HADOOP_ROOT]/conf</value>
</property>

leveraging OOZIE-792, this information can be set in Oozie's conf/hadoop-conf/hive.xml