Put Temp on RAM Disk for Azure Pipelines tests

Profiling on Azure Pipelines indicates that the majority of our time is
spent waiting for filesystem operations to complete. As a quick way to
improve our test speed in this area, we can do operations on a RAM disk
instead of the default SSDs.

.azure-pipelines/steps/run-tests-windows.yml

@@ -8,10 +8,62 @@ steps:
     versionSpec: '$(python.version)'
     architecture: '$(python.architecture)'
 
+- powershell: |
+    echo "Installing FS-iSCSITarget-Server"
+    Install-WindowsFeature -Name FS-iSCSITarget-Server
+
+    # Allow connection on loopback interface.
+    Set-ItemProperty -Path 'HKLM:\SOFTWARE\Microsoft\iSCSI Target' -Name AllowLoopBack -Value 1
+
+    echo "Starting MsiSCSI"
+    Start-Service msiscsi
+    $retry = 10
+    do
+    {
+      $count = (Get-Service msiscsi | ? {$_.status -eq "Running"}).count
+      $retry--
+      sleep -Milliseconds 500
+    } until ($count -Eq 0 -or $retry -Eq 0)
+
+    $service = Get-Service msiscsi
+    if ($service.Status -Ne "Running") {
+      throw "msiscsi not running"
+    }
+
+    echo "Configuring Firewall"
+    Get-NetFirewallServiceFilter -Service msiscsi | Enable-NetFirewallRule
+
+    echo "Configuring RAMDisk"
+    New-IscsiVirtualDisk -ComputerName localhost -Path ramdisk:RAMDISK1.vhdx -Size 1GB
+    New-IscsiServerTarget Target1 -ComputerName localhost -InitiatorId "IQN:*"
+    Add-IscsiVirtualDiskTargetMapping -ComputerName localhost -TargetName Target1 -Path ramdisk:RAMDISK1.vhdx -Lun 1
+
+    echo "Connecting to iSCSI"
+    $ip = (Get-NetIPAddress -AddressFamily IPv4).ipaddress[0]
+    New-IscsiTargetPortal -TargetPortalAddress $ip
+    Get-IscsiTarget | Connect-IscsiTarget
+
+    echo "Configuring disk"
+    Get-IscsiConnection | Get-Disk | Set-Disk -IsOffline $False
+    Get-IscsiConnection | Get-Disk | Initialize-Disk -PartitionStyle MBR
+    Get-IscsiConnection | Get-Disk | New-Partition -UseMaximumSize -DriveLetter R
+    Format-Volume -DriveLetter R -NewFileSystemLabel Temp -FileSystem NTFS
+
+    echo "Adding permissions"
+    mkdir R:\Temp
+    $acl = Get-Acl "R:\Temp"
+    $rule = New-Object System.Security.AccessControl.FileSystemAccessRule("Everyone", "FullControl", "ContainerInherit,ObjectInherit", "None", "Allow")
+    $acl.AddAccessRule($rule)
+    Set-Acl "R:\Temp" $acl
+  displayName: Setup RAM Disk
+
 - bash: pip install --upgrade setuptools tox
   displayName: Install Tox
 
-- script: tox -e py -- -m unit -n 3 --junit-xml=junit/unit-test.xml
+- script:
+    tox -e py -- -m unit --junit-xml=junit/unit-test.xml
+  env:
+    TEMP: "R:\\Temp"
   displayName: Tox run unit tests
 
 - ${{ if eq(parameters.runIntegrationTests, 'true') }}:
@@ -23,9 +75,7 @@ steps:
 
       # Shorten paths to get under MAX_PATH or else integration tests will fail
       # https://bugs.python.org/issue18199
-      subst T: $env:TEMP
-      $env:TEMP = "T:\"
-      $env:TMP = "T:\"
+      $env:TEMP = "R:\Temp"
 
       tox -e py -- -m integration -n 3 --duration=5 --junit-xml=junit/integration-test.xml
     displayName: Tox run integration tests