Add Python toolcache installation from Github releases for Ubuntu (#704)

Change logic to install Python to Ubuntu images to use GitHub releases from https://github.com/actions/python-versions

images/linux/scripts/installers/Validate-Toolset.ps1

@@ -0,0 +1,62 @@
+################################################################################
+##  File:  Validate-Toolset.ps1
+##  Team:  CI-Build
+##  Desc:  Validate Toolset
+################################################################################
+
+function Run-ExecutableTests {
+    param (
+        [Parameter(Mandatory)] [string[]] $Executables,
+        [Parameter(Mandatory)] [string] $ToolPath
+    )
+
+    foreach ($executable in $Executables) {
+        $executablePath = Join-Path $ToolPath $executable
+
+        Write-Host "Check $executable..."
+        if (Test-Path $executablePath) {
+            Write-Host "$executable is successfully installed: $(& $executablePath --version)"
+        } else {
+            Write-Host "$executablePath is not installed!"
+            exit 1
+        }
+    }
+}
+
+$ErrorActionPreference = "Stop"
+
+# Define executables for cached tools
+$toolsExecutables = @{ Python = @("python", "bin/pip") }
+
+# Get toolset content
+$toolsetJson = Get-Content -Path "$env:INSTALLER_SCRIPT_FOLDER/toolset.json" -Raw
+$tools = ConvertFrom-Json -InputObject $toolsetJson | Select-Object -ExpandProperty toolcache
+
+foreach($tool in $tools) {
+    Invoke-Expression "bash -c `"source $env:HELPER_SCRIPTS/document.sh; DocumentInstalledItem '$($tool.name):'`""
+
+    $toolPath = Join-Path $env:AGENT_TOOLSDIRECTORY $tool.name
+    # Get executables for current tool
+    $toolExecs = $toolsExecutables[$tool.name]
+
+    foreach ($version in $tool.versions) {
+        # Check if version folder exists
+        $expectedVersionPath = Join-Path $toolPath $version
+        if (-not (Test-Path $expectedVersionPath)) {
+            Write-Host "Expected $($tool.name) $version folder is not found!"
+            exit 1
+        }
+
+        # Take latest installed version in case if toolset version contains wildcards
+        $foundVersion = Get-Item $expectedVersionPath `
+                        | Sort-Object -Property {[version]$_.name} -Descending `
+                        | Select-Object -First 1
+        $foundVersionPath = Join-Path $foundVersion $tool.arch
+
+        Write-Host "Run validation test for $($tool.name)($($tool.arch)) $($foundVersion.name) executables..."
+        Run-ExecutableTests -Executables $toolExecs -ToolPath $foundVersionPath
+
+        # Add tool version to documentation
+        Invoke-Expression "bash -c `"source $env:HELPER_SCRIPTS/document.sh; DocumentInstalledItemIndent '$($tool.name) $($foundVersion.name)'`""
+    }
+}