Override the default deployment bucket name #236

Looks like we do not have any control over the cloud storage bucket for deployments. Parameterizing this would give user's finer control over IAM policies and permissions. For example, current deployments require storage.objects.get, storage.objects.list, storage.objects.create, & storage.objects.delete permissions. I would like to limit these permissions to a pre-defined bucket.

const name = `sls-${service}-${stage}-${timestamp}`;

this.serverless.service.provider.deploymentBucketName = name;