Fix for bug 1378926 - error 8448 with java.lang.OutOfMemoryError

Trafodion SQL processes dump java heap at $MY_SQROOT/logs in the
format java_pid<pid>.hprof when java.lang.OutOfMemoryError exception is
raised.

There were local references/global references that were not being deleted
in the trafodion code and that was causing leak in Java objects.

HTableClient_JNI objects are now cleaned up from the Java side if the
corresponding java objects are left in in-use pool at the time of ODBC/JDBC
disconnect. This takes care of memory leak on the C++ heap and java object
heap for such cases.

Change-Id: I799ed685ef0842ca1eebc9b55f146eaff2bd7729