azure-pipelines-yml: early exit on errors.

We don't want to silently ignore failing commands.

Also, while we're editing the `tap-new` generated `azure-pipelines.yml`
also add the changes missed here from #5600.

Library/Homebrew/dev-cmd/tap-new.rb

@@ -55,10 +55,11 @@ module Homebrew
       jobs:
       - job: macOS
         pool:
-          vmImage: xcode9-macos10.13
+          vmImage: macOS-10.13
         steps:
           - bash: |
-              sudo xcode-select --switch /Applications/Xcode_10.app/Contents/Developer
+              set -e
+              sudo xcode-select --switch /Applications/Xcode_10.1.app/Contents/Developer
               brew update
               HOMEBREW_TAP_DIR="/usr/local/Homebrew/Library/Taps/#{tap}"
               mkdir -p "$HOMEBREW_TAP_DIR"

azure-pipelines.yml

@@ -4,6 +4,7 @@ jobs:
     vmImage: macOS-10.13
   steps:
     - bash: |
+        set -e
         sudo xcode-select --switch /Applications/Xcode_10.1.app/Contents/Developer
         HOMEBREW_REPOSITORY="$(brew --repo)"
         mv "$HOMEBREW_REPOSITORY/Library/Taps" "$PWD/Library"
@@ -36,6 +37,7 @@ jobs:
     vmImage: ubuntu-16.04
   steps:
     - bash: |
+        set -e
         HOMEBREW_REPOSITORY=/home/linuxbrew/.linuxbrew
         sudo mkdir -p /home/linuxbrew
         sudo mv "$PWD" "$HOMEBREW_REPOSITORY"