Revert ill-considered change in pg_resetwal output.

Commit 31dcfae changed one pg_resetwal output string, and a
corresponding test in pg_upgrade, without sufficient thought for
the consequences.  We can't change that output without creating
hazards for cross-version upgrades, since pg_upgrade needs to be able
to read the output of several different versions of pg_resetwal.
There may well be external tools with the same requirement.

For the moment, just revert those two changes.  What we really
ought to do here is have a separate, stable, easily machine-readable
output format for pg_resetwal and pg_controldata, as proposed
years ago by Alvaro.  Once that's in place and tools no longer
need to depend on the exact spelling of the human-readable output,
we can put back this change.

Discussion: https://postgr.es/m/fbea8c6f-415a-bad9-c3de-969c40d08a84@dunslane.net

Author: tglsfdc

src/bin/pg_resetwal/pg_resetwal.c

@@ -788,7 +788,7 @@ PrintNewControlValues(void)
 
 	XLogFileName(fname, ControlFile.checkPointCopy.ThisTimeLineID,
 				 newXlogSegNo, WalSegSz);
-	printf(_("First WAL segment after reset:        %s\n"), fname);
+	printf(_("First log segment after reset:        %s\n"), fname);
 
 	if (set_mxid != 0)
 	{

src/bin/pg_upgrade/controldata.c

@@ -348,7 +348,7 @@ get_control_data(ClusterInfo *cluster, bool live_check)
 			cluster->controldata.chkpnt_nxtmxoff = str2uint(p);
 			got_mxoff = true;
 		}
-		else if ((p = strstr(bufin, "First WAL segment after reset:")) != NULL)
+		else if ((p = strstr(bufin, "First log segment after reset:")) != NULL)
 		{
 			/* Skip the colon and any whitespace after it */
 			p = strchr(p, ':');