Improve error handling for parse errors in embedded JDBC.
Break out a base class for the embedded JDBC IT.
That is enough to switch IndexScanUnboundedMixedOrderDT.
Adjust REST error reporting to extract embedded JDBC failures a little more consistently.
merge MMcM: Some cleanups in the embedded JDBC driver and its test

Merge pull request #1546 from MMcM/sql-layer/embedded-jdbc-for-tests-1
https://github.com/FoundationDB/sql-layer/pull/1546