Fix ServiceName issue for New-AzureVM

https://github.com/Azure/azure-sdk-tools/issues/1053

https://github.com/Azure/azure-sdk-tools/issues/1668
Fix relative path issue for Add-AzureVhd

https://github.com/Azure/azure-sdk-tools/issues/1710
Update of the help of New-AzureVM and New-AzureQuickVM
Merge pull request #120 from huangpf/dev

AzureRT Sprint S37
Merge pull request #121 from hyonholee/dev

Fix ServiceName issue for New-AzureVM