Fix error handling in artifacts{,/*} pkg

Fix error handling in artifacts{,/*} pkg

- Handled a few unhandled errors (reported by gas and errcheck).

Verification:
$ gometalinter.v2 --disable-all --vendor --enable=gas --enable=errcheck  ./artifacts/...

Should return no errors.

Some errors should just be logged and are logged via standard log
library.

Additionally call to getID function and the function itself were
removed. They were not neccessary after moving ID field to ArtifactInfo
struct.

Change-Id: If0d249aa08e296c7b46bc06532fe51d835e1b5c6
Signed-off-by: Alexander Mazuruk <a.mazuruk@samsung.com>