fix(packaging): capture xcatconfig stderr in the upgrade log

The RPM %post runs `xcatconfig -u -V >> /var/log/xcat/upgrade.log` with only
stdout redirected, so any errors or warnings the upgrade emits go to the
package manager's output and are lost from the log a later diagnosis relies
on.

Redirect stderr into the same log with 2>&1.

Recovered from the unmerged lenovobuild branch (original 51d87d4d).

Co-authored-by: Jarrod Johnson <10814490+jjohnson42@users.noreply.github.com>

xCAT/xCAT.spec

@@ -261,7 +261,7 @@ fi
 
 mkdir -p /var/log/xcat
 date >> /var/log/xcat/upgrade.log
-$RPM_INSTALL_PREFIX0/sbin/xcatconfig -u -V >> /var/log/xcat/upgrade.log
+$RPM_INSTALL_PREFIX0/sbin/xcatconfig -u -V >> /var/log/xcat/upgrade.log 2>&1
 fi
 exit 0