Start disabling caching if archive_dir is passed in.
Start disabling caching if archive_dir is passed in.

Made GenerateUpdateImage signature compatible with
GenerateUpdateImageWithCache again, and made WithCache
for forward the call if caching is disable.

Also sneaking in a small change to replace crosutils dir with scripts_dir which already existed.

Change-Id: I2d81d4b410880ec23e7f7c34f02563125325d330

BUG=chromium-os:8207
TEST=Tested normal behavior, not archive_dir.

Review URL: http://codereview.chromium.org/5224002

coreos/dev-util,marineam/coreos-dev-util,mgireesh05/dev-util,coreos/dev-util,coreos/dev-util,marineam/coreos-dev-util,mgireesh05/dev-util,mgireesh05/dev-util