Exclude ExplicitCollateNode from parser usage test.

Change due to #1565.
Remove a number of unsed references to rowtype schema.
Remove unused import
Remove unused import
Update ConncurrentTestBuilder to use RandomRule (with command line seed
option) to control test.
Make the IS Table scan generation use the AIS from the group, rather
than from the session AIS because they may not be identity equal (and
with the same underlying rowtype Schema). This has the potiential to
cause unexpected failures.
Update and add new tests for Overlapping DDL and DML to verify the
processing works correctly.
Merge remote-tracking branch 'github/master' into Overlapping-dml-ddl-race-condition
merge nathanlws: Exclude ExplicitCollateNode from parser usage test.

Merge pull request #1569 from nathanlws/sql-layer/parser-check-exclude-collationnode
https://github.com/FoundationDB/sql-layer/pull/1569
merge tjoneslo: Overlapping dml ddl race condition

Merge pull request #1572 from tjoneslo/sql-layer/Overlapping-dml-ddl-race-condition
https://github.com/FoundationDB/sql-layer/pull/1572
Extend tracking of isolation levels through to the transaction service, where something interesting might happen.
Centralize selection of transaction scan options for operator.
Hook those together so that SET TRANSACTION ISOLATION LEVEL selects appropriate scan options for operators.
Allow getting scan options without a transaction for tests that create cursors and only then begin before opening them.
Need a getSnapshotFuture.
Add new isolation levels for embedded JDBC using negative ints.
Make default schema in embedded JDBC more reliable.
That new overload was a bad idea.
Also check before starting iterator, for the case of multiple statements.
Add snapshot IT showing that whereas serializable conflicts, this skews.
Add read committed IT showing that "long" scans complete with expected isolation violations.