Windows: fix Golang version checks for GO_VERSION build-arg

This check was used to make sure we don't bump Go versions independently
(Linux/Windows). The Dockerfile switched to using a build-arg to allow
overriding the Go version, which rendered this check non-functional.

It also fails if Linux versions use a specific variant of the image;

08:41:31 ERROR: Failed 'ERROR: Mismatched GO versions between Dockerfile and Dockerfile.windows. Update your PR to ensure that both files are updated and in sync. ${GO_VERSION}-stretch ${GO_VERSION}' at 07/20/2019 08:41:31
08:41:31 At C:\gopath\src\github.com\docker\docker\hack\ci\windows.ps1:448 char:9
08:41:31 +         Throw "ERROR: Mismatched GO versions between Dockerfile and D ...
08:41:31 +         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This patch fixes the check by looking for the value of `GO_VERSION` instead
of looking at the `FROM` line (which is harder to parse).

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

hack/ci/windows.ps1

@@ -426,20 +426,9 @@ Try {
     Write-Host -ForegroundColor Green "INFO: Location for testing is $env:TEMP"
 
     # CI Integrity check - ensure Dockerfile.windows and Dockerfile go versions match
-    $goVersionDockerfileWindows=$(Get-Content ".\Dockerfile.windows" | Select-String "^ENV GO_VERSION" | Select-object -First 1).ToString().Replace("ENV GO_VERSION=","").Replace("\","").Replace("``","").Trim()
-    $goVersionDockerfile=$(Get-Content ".\Dockerfile" | Select-String "^ENV GO_VERSION" | Select-object -First 1)
-    
-    # As of go 1.11, Dockerfile changed to be in the format like "FROM golang:1.11.0 AS base".
-    # If a version number ends with .0 (as in 1.11.0, a convention used in golang docker
-    # image versions), it needs to be removed (i.e. "1.11.0" becomes "1.11").
-    if ($null -eq $goVersionDockerfile) {
-        $goVersionDockerfile=$(Get-Content ".\Dockerfile" | Select-String "^FROM golang:" | Select-object -First 1)
-        if ($null -ne $goVersionDockerfile) {
-            $goVersionDockerfile = $goVersionDockerfile.ToString().Split(" ")[1].Split(":")[1] -replace '\.0$',''
-        }
-    } else {
-        $goVersionDockerfile = $goVersionDockerfile.ToString().Split(" ")[2]
-    }
+    $goVersionDockerfileWindows=(Select-String -Path ".\Dockerfile.windows" -Pattern "^ARG[\s]+GO_VERSION=(.*)$").Matches.groups[1].Value
+    $goVersionDockerfile=(Select-String -Path ".\Dockerfile" -Pattern "^ARG[\s]+GO_VERSION=(.*)$").Matches.groups[1].Value
+
     if ($null -eq $goVersionDockerfile) {
         Throw "ERROR: Failed to extract golang version from Dockerfile"
     }

hack/make.ps1

@@ -134,7 +134,7 @@ Function Check-InContainer() {
 # outside of a container where it may be out of date with master.
 Function Verify-GoVersion() {
     Try {
-        $goVersionDockerfile=(Select-String -Path ".\Dockerfile" -Pattern "^FROM golang:").ToString().Split(" ")[1].SubString(7) -replace '\.0$',''
+        $goVersionDockerfile=(Select-String -Path ".\Dockerfile" -Pattern "^ARG[\s]+GO_VERSION=(.*)$").Matches.groups[1].Value.TrimEnd(".0")
         $goVersionInstalled=(go version).ToString().Split(" ")[2].SubString(2)
     }
     Catch [Exception] {