Make docker::machine::url configurable

As docker machine is now in maintanence mode [1] there are forks of it
where people might want to download the binary from.

[1]: docker/machine#4537

Author: baurmatt

manifests/machine.pp

@@ -20,11 +20,15 @@
 # [*proxy*]
 #   Proxy to use for downloading Docker Machine.
 #
+# [*url*]
+#   The URL from which the docker machine binary should be fetched
+#   Defaults to a auto determined value based on version, kernel and OS.
 class docker::machine(
-  Optional[Pattern[/^present$|^absent$/]] $ensure          = 'present',
-  Optional[String] $version                                = $docker::params::machine_version,
-  Optional[String] $install_path                           = $docker::params::machine_install_path,
-  Optional[String] $proxy                                  = undef
+  Optional[Pattern[/^present$|^absent$/]]              $ensure       = 'present',
+  Optional[String]                                     $version      = $docker::params::machine_version,
+  Optional[String]                                     $install_path = $docker::params::machine_install_path,
+  Optional[String]                                     $proxy        = undef,
+  Optional[Variant[Stdlib::HTTPUrl, Stdlib::HTTPSUrl]] $url          = undef,
 ) inherits docker::params {
 
   if $proxy != undef {
@@ -43,7 +47,10 @@
   $docker_machine_location_versioned = "${install_path}/docker-machine-${version}${file_extension}"
 
   if $ensure == 'present' {
-    $docker_machine_url = "https://github.com/docker/machine/releases/download/v${version}/docker-machine-${::kernel}-x86_64${file_extension}"
+    $docker_machine_url = $url ? {
+      undef   => "https://github.com/docker/machine/releases/download/v${version}/docker-machine-${::kernel}-x86_64${file_extension}",
+      default => $url,
+    }
 
     if $proxy != undef {
       $proxy_opt = "--proxy ${proxy}"

spec/classes/machine_spec.rb

@@ -113,4 +113,20 @@
       )
     }
   end
+
+  context 'with docker_machine_url is provided' do
+    let(:params) do
+      {
+        version: '0.16.2',
+        url: 'https://gitlab-docker-machine-downloads.s3.amazonaws.com/v0.16.2-gitlab.3/docker-machine',
+      }
+    end
+
+    it { is_expected.to compile }
+    it {
+      is_expected.to contain_exec('Install Docker Machine 0.16.2').with_command(
+        'curl -s -S -L  https://gitlab-docker-machine-downloads.s3.amazonaws.com/v0.16.2-gitlab.3/docker-machine -o /usr/local/bin/docker-machine-0.16.2',
+      )
+    }
+  end
 end