Change names of a couple of variables realted to
command id exchange mechanism to more general names.
Fix for test case with.sql

There were two issues making the test to fail.
1. Updates to partition column were possible using syntax like
   WITH t AS (UPDATE y SET a=a+1 RETURNING *) SELECT * FROM t
   The patch blocks this syntax.

2. For a WITH query that updates a table in the main query and
   inserts a row in the same table in the WITH query we need to use
   command ID communication to remote nodes in order to
   maintain global data visibility.
   Similarly a WITH query that deletes from a parent table in the
   main query & inserts a row in the child table in the WITH query
   we need to use command ID communication to remote nodes in order
   to maintain global data visibility.
This commit adds gtm capability to backup its restart point according
to CREATE BARRIER statement.

Runs without GTM-Proxy now.