pg_upgrade: prevent check on live cluster from generating error

Bruce Momjian <bruce@momjian.us>

Commit: 1776c817c7ef452fb47d915d1b550cd73a318944
Author: Bruce Momjian <bruce@momjian.us>
Date: 2018-01-09T03:43:51Z
Releases: 10.2
pg_upgrade:  prevent check on live cluster from generating error

Previously an inaccurate but harmless error was generated when running
--check on a live server before reporting the servers as compatible.
The fix is to split error reporting and exit control in the exec_prog()
API.

Reported-by: Daniel Westermann

Backpatch-through: 10

Files