Bug fixes fir bulk unload

- 1398981 unload with union query fails with ERROR[4066]
- 1392481 UNLOAD query involves ORDER-BY returns ERORR[4001]
- By addressing these 2 issues the parser problem we faced before
  where we could not use query_expression with UNLOAD is now
  also fixed without any additinal conflicts

Change-Id: Ia3a724ac21f77e596a4db559781de5146fe208c6
Merge "Bug fixes fir bulk unload"