Add --save_config and --set_config options to make_dev_ssd.sh

Add --save_config and --set_config options to make_dev_ssd.sh

Change-Id: I691e6e62f5d5d9b6671fd05f172829b84d503b77

BUG=9934
TEST=manual

1. From a root shell, on a device signed with developer keys:
  make_dev_ssd.sh --save_config=foo

This should create a foo.2 file with a kernel command line.  It'll be
similar to the one in /proc/cmdline.  It may create a foo.4 file, if
kernel B is also valid.

2. Modify the command line in foo.2 (and foo.4, if it exists).
Suggest adding "blah2" to foo.2, and "blah4" to foo.4 if it
exists.

3. From a root shell:
  make_dev_ssd.sh --set_config=foo

4. Reboot.

5. Check the kernel command line.
  cat /proc/cmdline

If you booted from kernel A, you should see "blah2" in the command
line.  If B, you should see "blah4".

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=38ab919

[Bill Richardson, 2010-12-03 16:16:40]

LGTM with one nit.

http://codereview.chromium.org/5567003/diff/1/scripts/image_signing/make_dev_...
File scripts/image_signing/make_dev_ssd.sh (right):

http://codereview.chromium.org/5567003/diff/1/scripts/image_signing/make_dev_...
scripts/image_signing/make_dev_ssd.sh:137: then
Style nit: use "if blahblah; then" on one line.