Job/Flow/Riffle refactoring

- Export/DeleteAndExport/Import share common Flow and Riffle
- Added deleteAndExportSqoop methods to Sqoop Execution
- Added ExportSqoopSpec
- Renamed SqoopImportSpec to ImportSqoopSpec
Yes, we are setting exportDir, escapedBy, inputFieldsTerminatedBy with values infered from source tap.