image_to_vm.sh: Switch default VM layout to "2gb-rootfs-updatable".

We now have VM tests that need more space. We were increasing the
layout in cbuildbot, but it seems better to change the default so that
everyone is more likely to do the same thing.

BUG=chromium:404858
TEST=Local build + PreCQ.

Change-Id: I3ce97fadc5859f6fb09af0228b739ea53a4be8a1
Reviewed-on: https://chromium-review.googlesource.com/214114
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Don Garrett <dgarrett@chromium.org>
diff --git a/image_to_vm.sh b/image_to_vm.sh
index 22bce4e..1b9dc47 100755
--- a/image_to_vm.sh
+++ b/image_to_vm.sh
@@ -36,7 +36,7 @@
   "Output format, either qemu, vmware or virtualbox"
 DEFINE_string from "" \
   "Directory containing rootfs.image and mbr.image"
-DEFINE_string disk_layout "usb" \
+DEFINE_string disk_layout "2gb-rootfs-updatable" \
   "The disk layout type to use for this image."
 DEFINE_boolean make_vmx ${FLAGS_TRUE} \
   "Create a vmx file for use with vmplayer (vmware only)."