Add the ability to resolve cached artifacts from remote Nuget repository in case the remote repository is down.
Currently in case the remote repository went down, when the client will try to resolve an artifact, Artifactory will will query the remote repository for metadata information and since it unreachable, will not find the relevant information and will not be able to provide the client with an artifact even if it cached.
steps to reproduce (using two Artifactory servers):
1. create nuget remote repository from Art1 to Art2.
2. download artifact using the remote repository from step 1 (using Nuget client).
3. take down the server Art2.
4. try to download the artifact from step 2 again (using Nuget client).