Rename image re-signing utility (for compactness and consistency sake).

Review URL: http://codereview.chromium.org/3027027
diff --git a/scripts/image_signing/cros_resign_image_standalone.sh b/scripts/image_signing/resign_image.sh
similarity index 100%
rename from scripts/image_signing/cros_resign_image_standalone.sh
rename to scripts/image_signing/resign_image.sh