Allow atmos unsupported versions

When I'm trying to connect to our atmos blobstore I get the following error:
```
Bosh::Blobstore::BlobstoreError: Failed to create object, underlying error: 
#<Atmos::Exceptions::NotImplementedException: 
This library does not support Atmos version 2.1.5.0.  
Supported versions: ["1.2.7", "1.3.4", "1.4.0", "1.4.1", "1.4.2", "2.0.1"].  
To silence this, pass :unsupported => true when instantiating.
```

Since the blobstore-client already uses the latest version of [ruby-atmos-pure](the https://rubygems.org/gems/ruby-atmos-pure) gem the only option was to use the `:unsupported => true`.