crosutils/make_factory_package.sh: support full SSD image as target outside chroot

crosutils/make_factory_package.sh: support full SSD image as target outside chroot

When running outside chroot, we should use locate_cgpt + "$GPT" to invoke cgpt;
otherwise it may be not in system PATH.

For dealing with a true SSD image (over USB, for example) this CL also improved
data writing speed from <2M/s to 8M/s+ (over USB).

BUG=chromium-os:10531
TEST=./make_factory_package.sh \
  --factory=../build/images/x86-mario/latest/chromiumos_factory_image.bin \
  --release=../build/images/x86-mario/latest//chromiumos_image.bin \
  --diskimg=/dev/sdb

Also tested:
  --diskimg=blah # local file
  (chroot) --diskimg=/dev/sdd 
  (chroot) --diskimg=blah

Change-Id: I647d97fe388f5b6a6223fa8cacfecdf00265f60c

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=4653cbd

[Nick Sanders, 2011-01-13 08:35:32]

lgtm. Please also test writing output to a file before submit. Please note
whether inside/outside chroot has been tested

[Nick Sanders, 2011-01-13 08:55:54]

Can you also cherry pick these to 0.9.132.B?

[Hung-Te, 2011-01-14 03:20:43]

On 2011/01/13 08:55:54, Nick Sanders wrote:
> Can you also cherry pick these to 0.9.132.B?
Done.