feature TDI-29674 : Teradata: ELT enhancements
Fix problems:
1. move the store/restore functions from Connection.java to the
*Command.java
2. modify the PostgresGenerationManagerTest.java to fit the modification
for subquery.
Fix problem:
when undo a connection create action, null pointer exception will be
happened
Fix problem:
 When using context value, the quotation marks for const strings can not
be added correctly