Change default operation to "rename", previously we were not renaming or

purging the image files. Have not noticed, since we pass purge option
in most places.

utils/delete_image.in

 #!/usr/bin/perl -w
 #
-# Copyright (c) 2000-2015 University of Utah and the Flux Group.
+# Copyright (c) 2000-2017 University of Utah and the Flux Group.
 # 
 # {{{EMULAB-LICENSE
 # 
@@ -35,7 +35,7 @@ sub usage()
     print("Usage: delete_image [[-f | -F] -p | -r] <imagename>\n".
 	  "Options:\n".
 	  "       -p     Purge the disk image file(s)\n".
-	  "       -r     Rename the disk image file(s) instead\n".
+	  "       -r     Rename the disk image file(s) instead (default)\n".
 	  "       -n     Impotent mode, show what would be done.\n".
 	  "       -f     Force deletion of system image\n".
 	  "       -F     Force deletion of global system image\n");
@@ -44,7 +44,7 @@ sub usage()
 my $optlist     = "dFprnf";
 my $debug       = 0;
 my $purge       = 0;
-my $rename      = 0;
+my $rename      = 1;
 my $force       = 0;
 my $FORCE       = 0;
 my $impotent    = 0;
@@ -105,7 +105,8 @@ if (defined($options{"d"})) {
     $debug = 1;
 }
 if (defined($options{"p"})) {
-    $purge = 1;
+    $purge  = 1;
+    $rename = 0;
 }
 if (defined($options{"r"})) {
     $rename = 1;