Move Pester to submodule to Host/Modules

This way it can also be deployed automatically, removing the last manual
copy steps from our build scripts.

Travis and AppVeyor configurations updated for new submodule location.

appveyor.yml

@@ -13,7 +13,7 @@ install:
   - ps: $fileContent += "`n-----END RSA PRIVATE KEY-----`n"
   - ps: Set-Content c:\users\appveyor\.ssh\id_rsa $fileContent
   - git config --global url.git@github.com:.insteadOf https://github.com/
-  - git submodule update --init --recursive -- src/monad src/windows-build test/Pester
+  - git submodule update --init --recursive -- src/monad src/windows-build src/Microsoft.PowerShell.Linux.Host/Modules/Pester
   - ps: Invoke-WebRequest -Uri https://dotnetcli.blob.core.windows.net/dotnet/dev/Binaries/Latest/dotnet-win-x64.latest.zip -OutFile dotnet.zip
   - 7z x dotnet.zip -odotnet > nul