Eng 6390 jdbc resultset

Wrote the test cases (as per issue description) for HSQL JDBCResultSet and VoltDB JDBC4ResultSet (for Empty and Non-Empty tables) and compared the corresponding results.

Fixed the cursor navigations in the scrollable JDBC4ResultSet for forward and backward navigations and all the boundary cases.
I think that checking enum won't make a difference here because we need to check is cursor is at first if yes then return true otherwise in any other case return false.
Same is applicable for isLast() method also.