support using existing azure file share in storage class

[andyzhangx]

Is your feature request related to a problem?/Why is this needed

Describe the solution you'd like in detail

scenario is like this:
https://github.com/csi-driver/blobfuse-csi-driver#option1-use-existing-credentials-in-k8s-cluster

Need to add a new parameter(shareName) in azure file storage class, and create an azure file if it does not exist:

azurefile-csi-driver/pkg/azurefile/controllerserver.go

Line 90 in 224a7d3

retAccount, _, err := d.cloud.CreateFileShare(fileShareName, account, sku, accountKind, resourceGroup, location, requestGiB)

Describe alternatives you've considered

Additional context

/assign

[ashishranjan738]

I think i can take this up

[andyzhangx]

it's not a urgent feature, let me change the interface in azure cloud provider first since currently it still uses func (s *Share) Create(options *FileRequestOptions) other than func (s *Share) CreateIfNotExists(options *FileRequestOptions) func

[lenisha]

we have a scenario to mount azure files using the cluster identity or secrets coming from Vault

[andyzhangx]

The PR(kubernetes/kubernetes#77042) is already merged in v1.14.2, upgrade to use that lib and a few code change could make this feature work.