Consider more stable approach when checking if local artifacts were copied to storage

[gboyvalenkov-bosch]

Currently, there is a validation in feature_test.go, in testDownloadInstall function, that does two checks in the worst case:

1. Whether a non-copy artifact is moved to storage or not. In case the storage folder does not exist, the next check is done.
2. Whether this artifact is copied in modules folder or not.

Since the two possible outcomes are possible, the behavior of download operation must be checked, whether it does synchronous or asynchronous moving of files. The test case should be fixed accordingly to ensure more deterministic behavior upon each execution.