Support Set-AzureRMstorageAccount with Kind StorageV2

[blueww]

Description

We have already added StorgeV2 support in New-AzureRMStorageAccount.
And this PR add StorageV2 support to Set-AzureRMstorageAccount.

Only Storage/BlobStorage->StorageV2 is supported,
StorageV2->BlobStorage/Storage, BlobStorage<->Storage are not supported by server.

So the validSet of -Kind for Set-AzureRMstorageAccount only has 1 value "StorageV2"
We keep the -Kind in Set-AzureRMstorageAccount as one value allowed string parameter instead of switch parameter, since:

1. Avoid breaking when add new support kind in the future like StorageV3...
2. would like to keep the usage of it aligned with the "-Kind" parameter of Add-AzureRMstorageAccount

---

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[blueww]

On -Demand: https://azuresdkci.westus2.cloudapp.azure.com/view/PowerShell/job/powershell-demand/270/

[blueww]

Run on-demand again with "-UpgradeToStorageV2" change:
https://azuresdkci.westus2.cloudapp.azure.com/view/PowerShell/job/powershell-demand/275/

[markcowl]

@blueww Please update the version of the module in AzureRM.Storage.psd1 (should be 4.1.0), please add the text here to the 'ReleaseNotes' in AzureRM.Storage.psd1, and please update the AssemblyVersion and AssemblyFileVersion in AssemblyInfo.cs for the built assembly (Microsoft.Azure.Commands.Management.Storage).

Otherwise, this looks good.

[blueww]

@markcowl
All updated. Please check.

[blueww]

run on-demand again with version update: https://azuresdkci.westus2.cloudapp.azure.com/view/PowerShell/job/powershell-demand/277/

[markcowl]

on demand run here: https://azuresdkci.westus2.cloudapp.azure.com/view/PowerShell/job/powershell-demand/278/

signing run here: https://azuresdkci.westus2.cloudapp.azure.com/view/PowerShell/job/powershell-sign/48/