Pull in XCATROOT more relably

the XCATROOT env variable might not be set.  For this case, pull
in the more reliable $::XCATROOT

xCAT-server/lib/perl/xCAT/Template.pm

@@ -1577,6 +1577,7 @@ sub envvar
     if ($envvar =~ /^\$/) {
         $envvar =~ s/^\$//;
     }
+    if ($envvar eq 'XCATROOT') { return $::XCATROOT; }
 
     return ($ENV{$envvar});
 }