Bypass scan if cache entry is found

[fraxken]

When running commands such as auto, cwd and from we always scan even if the package has been registered in the local system cache.

The idea would be to improve that be skipping the scan step and just returning the JSON if it exist in the cache.

However some problem may arise with current Scanner API:

• from integrate the pacote.manifest call and we have no control on it. So for a given package name we have no idea if the latest match with what we have in local cache.
• same with CWD as we currently have no HASH signature of the package.json cached.

[clemgbld]

See: NodeSecure/scanner#554