image_signing: convert_recovery_to_ssd.sh: rewrite to be better

This converts the script in one commit as nothing uses it directly,
so the chances of it breaking overall build is low.
- Convert to common.sh for more helpers
- Convert echo to info
- Convert to loopback devices to speed things up
- Fix quoting in a few places
- Drop cgpt usage since we use loopback partitions everywhere now

BRANCH=None
BUG=chromium:714598
TEST=running on an image still works

Change-Id: I6608db77792502f35522a6f793ccd800fdd6af4e
Reviewed-on: https://chromium-review.googlesource.com/505482
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: David Riley <davidriley@chromium.org>
1 file changed