Make plan_node_id assignments in ORCA 0-based
Make plan_node_id assignments in ORCA 0-based

This is a follow-up to 0ae90045c7, which made plan_node_id assignments
in the server 0-based. The commit also changed gpperfom's explicit
dependencies on 1-based plan_node_ids to 0-base. This led to the
following gpperfmon behave test failing in CI for when ORCA is
enabled.

```
Then wait until the results from boolean sql "SELECT rows_out =
count(distinct content) from queries_history, gp_segment_configuration
where query_text like 'select gp_segment_id, count(*)%' and db =
'gptest' and content != -1 group by rows_out" is "true"
```

This commit fixes this failure by ensuring plan_node_ids start at 0,
with the root plan node getting an id 0 for ORCA plans.

Co-authored-by: Hao Wang <635f9f244095b81db40150c84907dd49a5db55fb@pivotal.io>
Co-authored-by: Jesse Zhang <6775950e159d0bc2e58935ca2201ba88526dddf0@pivotal.io>

50wu/gpdb,jmcatamney/gpdb,50wu/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,lisakowen/gpdb,jmcatamney/gpdb,lisakowen/gpdb,ashwinstar/gpdb,adam8157/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,50wu/gpdb,lisakowen/gpdb,xinzweb/gpdb,ashwinstar/gpdb,adam8157/gpdb,adam8157/gpdb,adam8157/gpdb,50wu/gpdb,lisakowen/gpdb,ashwinstar/gpdb,adam8157/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,50wu/gpdb,50wu/gpdb,xinzweb/gpdb,50wu/gpdb,greenplum-db/gpdb,adam8157/gpdb,xinzweb/gpdb,adam8157/gpdb,xinzweb/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,xinzweb/gpdb,xinzweb/gpdb,ashwinstar/gpdb,50wu/gpdb,adam8157/gpdb,lisakowen/gpdb,lisakowen/gpdb,lisakowen/gpdb,xinzweb/gpdb,xinzweb/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,lisakowen/gpdb,ashwinstar/gpdb