Make local copy of client hostnames in backend status array.
Make local copy of client hostnames in backend status array.

The other strings, application_name and query string, were snapshotted to
local memory in pgstat_read_current_status(), but we forgot to do that for
client hostnames. As a result, the client hostname would appear to change in
the local copy, if the client disconnected.

Backpatch to all supported versions.

Author: Edmund Horner
Reviewed-by: Michael Paquier
Discussion: https://www.postgresql.org/message-id/CAMyN-kA7aOJzBmrYFdXcc7Z0NmW%2B5jBaf_m%3D_-77uRNyKC9r%3DA%40mail.gmail.com

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