added a hook for the custom mod.tgz that if its already there not to update it, because it may have other updates in it already

git-svn-id: https://svn.code.sf.net/p/xcat/code/xcat-core/trunk@7077 8638fb3e-16cb-4fca-ae20-7b5d299a9bcd

xCAT-server/lib/xcat/plugins/esx.pm

@@ -2880,6 +2880,9 @@ sub copycd {
 sub  makecustomizedmod {
     my $osver = shift;
     my $dest = shift;
+    # if it already exists, do not overwrite it because it may be someone
+    # else's custom image
+    if(-f "$dest/mod.tgz"){ return 1; }
     my $passtab = xCAT::Table->new('passwd');
     my $tmp;
     my $password;