Resolve two minor review comments.

Rework of 1329965 fix:
Alternative fix involves replacing <col> in the key predicate:
_SALT_ = hash2partfunc(<col>...) with the actual constant matched in a user predicate.
We do this by adding valueIdMap between VegRefs of <col> and constant.
Doing this would make most of the earlier changes unnecessary, so backed out old changes.

Fixes for bugs 1326103 1329965.
bug 1326103 fix:
When Enforcer rule of Exchange operator fired, it creates a context for its child HBASE_SCAN.
Exchange operator doesn't send any partition requirement HBASE_SCAN, only sends location requirement.
Since PartRequirement is NULL, during Hbase synthesize physical properties, the logic to compute
desired DoP always takes "nodes" (number of nodes in the cluster) as minium DoP for Esp.
The fix is to use DoP computed based an table size as minimum value.

files:
sql/optimizer/OptPhysRelExpr.cpp
sql/sqlcomp/DefaultConstants.h
sql/sqlcomp/nadefaults.cpp

bug 1329965 fix:
While building SearchKey, optimizer recognizes  "_SALT_"  is a computed column and generates a
Key Predicate ._SALT_ = Hash(C1).. But later on it checks whether newly generated predicate is a key predicate,
this check fails because there is no VEG (Value equality group) between VarChar column C1 and constant "xyz".

Files:
sql/generator/GenPreCode.cpp
sql/optimizer/ValueDesc.cpp
sql/optimizer/ValueDesc.h
sql/optimizer/mdam.cpp
sql/optimizer/mdamkey.h

Change-Id: I9cf21bcbe54845611ab9024bcb3caefc6d8bac7c
Merge "Resolve two minor review comments."