Template sql-alwayson-md-mult-subnets-zones not deploying completely

[sql-alwayson-md-mult-subnets-zones](https://github.com/Azure/azure-quickstart-templates/tree/master/sql-alwayson-md-mult-subnets-zones)

### Issue Details
Trying to deploy a SQL cluster in AV zones.
VMs deploy correctly.
VM1 and VM2 deploy correctly and configure correctly (DSC).
VM0 doesn't deploy correctly and fails on DSC step. The DSC step times out and logs show an issue with a assembly loading.

###Logs
File: C:\WindowsAzure\Logs\Plugins\Microsoft.Powershell.DSC\2.76.0.0\DscExtensionHandler.0.20180622-063515
(FYI: this error appears multiple times)
```
VERBOSE: [2018-06-22 06:48:35Z] [VERBOSE] [wbsql-sql-0]:
[[xSqlLogin]AddDomainAdminAccountToSysadminServerRole] Error occured:
Error occured: 'Cannot find type
[Microsoft.SqlServer.Management.Common.ServerConnection]: verify that the
assembly containing this type is loaded.', failed after '13' times, retry for
'13' times
VERBOSE: [2018-06-22 06:48:35Z] Settings handler status to 'transitioning'
(C:\Packages\Plugins\Microsoft.Powershell.DSC\2.76.0.0\Status\0.status)
```

@wesback

Start with the sql-alwayson-md-mult-subnets-zones template and the Microsoft.Powershell.DSC DscExtensionHandler log at C:\WindowsAzure\Logs\Plugins\Microsoft.Powershell.DSC\2.76.0.0. Reproduce the deployment and trace the xSqlLogin AddDomainAdminAccountToSysadminServerRole step on VM0, focusing on the missing ServerConnection assembly. Done means VM0 completes DSC and the SQL cluster deploys successfully.

Written by the indexing model from the issue text.