(MODULES-8748) Use latest PowerShell Core versions in CI

Previously the default installed versions of PowerShell Core were used in Travis
CI and Appveyor.  This commit updates the CI configuration files to use the
latest stable release of PowerShell Core, using the same bootstrapping files the
PowerShell team uses [1].

[1] https://github.com/PowerShell/PowerShell/tree/master/tools

Author: glennsarti

.sync.yml

@@ -27,10 +27,9 @@ spec/default_facts.yml:
 .travis.yml:
   unmanaged: true
 
+# Due to https://github.com/puppetlabs/pdk-templates/issues/229 we can't manage Appveyor yet.
 appveyor.yml:
-  test_script:
-  - pwsh -NoProfile -NoLogo -NonInteractive -Command $PSVersionTable
-  - powershell -NoProfile -NoLogo -NonInteractive -Command $PSVersionTable
+  unmanaged: true
 
 .gitlab-ci.yml:
   delete: true

.travis.yml

@@ -11,19 +11,7 @@ language: ruby
 cache: bundler
 before_install:
   # Additional instructions
-  # Install PowerShell Core for Ubuntu 14.04
-  # There's an intermittent minor issue with the public key so just reset it with apt-key ... - https://github.com/git-lfs/git-lfs/issues/3474
-  - if [ $TRAVIS_OS_NAME == "linux" ]; then
-      curl https://packages.microsoft.com/keys/microsoft.asc | sudo apt-key add -;
-      curl https://packages.microsoft.com/config/ubuntu/14.04/prod.list | sudo tee /etc/apt/sources.list.d/microsoft.list;
-      sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6B05F25D762E3157;
-      sudo apt-get update;
-      sudo apt-get install -y powershell;
-    fi
-  # Install PowerShell Core for Mac
-  - if [ $TRAVIS_OS_NAME == "osx" ]; then
-      brew cask install powershell;
-    fi
+  - bash <(curl -s https://raw.githubusercontent.com/PowerShell/PowerShell/master/tools/install-powershell.sh) -skip-sudo-check
   # Output the PowerShell Core version information
   - pwsh -NoProfile -NoLogo -NonInteractive -Command \$PSVersionTable
   - if [ $BUNDLER_VERSION ]; then

appveyor.yml

@@ -39,15 +39,18 @@ install:
   - set PATH=C:\Ruby%RUBY_VERSION%\bin;%PATH%
   - bundle install --jobs 4 --retry 2 --without system_tests
   - type Gemfile.lock
+  - ps: "[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12; Invoke-WebRequest -Uri https://github.com/PowerShell/PowerShell/raw/master/tools/install-powershell.ps1 -UseBasicParsing -OutFile install-pwsh.ps1"
+  - ps: "& ./install-pwsh.ps1"
+  - set PATH=%LOCALAPPDATA%\Microsoft\powershell;%PATH%
+  - pwsh -NoProfile -NoLogo -NonInteractive -Command $PSVersionTable
+  - powershell -NoProfile -NoLogo -NonInteractive -Command $PSVersionTable
 build: off
 test_script:
   - bundle exec puppet -V
   - ruby -v
   - gem -v
   - bundle -v
   - bundle exec rake %CHECK%
-  - pwsh -NoProfile -NoLogo -NonInteractive -Command $PSVersionTable
-  - powershell -NoProfile -NoLogo -NonInteractive -Command $PSVersionTable
 notifications:
   - provider: Email
     to: