postgres_fdw: Fix tests with ANALYZE and remote sampling

postgres_fdw: Fix tests with ANALYZE and remote sampling

The tests fixed in this commit were changing the sampling setting of a
foreign server, but then were analyzing a local table instead of a
foreign table, meaning that the test was not running for its original
purpose.

This commit changes the ANALYZE commands to analyze the foreign table,
and changes the foreign table definition to point to a valid remote
table.  Attempting to analyze the foreign table "analyze_ftable" would
have failed before this commit, because "analyze_rtable1" is not defined
on the remote side.

Issue introduced by 8ad51b5f446b.

Author: Corey Huinker <corey.huinker@gmail.com>
Discussion: https://postgr.es/m/CADkLM=cpUiJ3QF7aUthTvaVMmgQcm7QqZBRMDLhBRTR+gJX-Og@mail.gmail.com
Backpatch-through: 16