[Azure Pipelines] Use `DEVELOPER_DIR` environment variable instead of executing `xcode-select`

That reduces some steps.

azure-pipelines.yml

@@ -65,26 +65,26 @@ jobs:
     maxParallel: 10
     matrix:
       xcode901:
-        XCODE_APP: 'Xcode_9.0.1'
+        DEVELOPER_DIR: /Applications/Xcode_9.0.1.app
       xcode91:
-        XCODE_APP: 'Xcode_9.1'
+        DEVELOPER_DIR: /Applications/Xcode_9.1.app
       xcode92:
-        XCODE_APP: 'Xcode_9.2'
+        DEVELOPER_DIR: /Applications/Xcode_9.2.app
       xcode931:
-        XCODE_APP: 'Xcode_9.3.1'
+        DEVELOPER_DIR: /Applications/Xcode_9.3.1.app
       xcode941:
-        XCODE_APP: 'Xcode_9.4.1'
+        DEVELOPER_DIR: /Applications/Xcode_9.4.1.app
       xcode10:
-        XCODE_APP: 'Xcode_10'
+        DEVELOPER_DIR: /Applications/Xcode_10.app
         XCODE_FLAGS_FOR_TEST: -parallel-testing-enabled NO
       xcode101:
-        XCODE_APP: 'Xcode_10.1'
+        DEVELOPER_DIR: /Applications/Xcode_10.1.app
         XCODE_FLAGS_FOR_TEST: -parallel-testing-enabled NO
   steps:
     - script: |
-        sudo xcode-select -s /Applications/$XCODE_APP.app
+        xcodebuild -version
         echo "##vso[task.setvariable variable=XCODE_FLAGS]-scheme Yams $XCODE_FLAGS_FOR_TEST"
-      displayName: xcode-select & set XCODE_FLAGS
+      displayName: xcodebuild -version & set XCODE_FLAGS
     - script: >
         set -o pipefail &&
         xcodebuild $XCODE_FLAGS test |
@@ -141,18 +141,18 @@ jobs:
 - job: CocoaPods
   pool:
     vmImage: 'macOS 10.13'
+  variables:
+    DEVELOPER_DIR: /Applications/Xcode_9.4.1.app
   steps:
-    - script: sudo xcode-select -s /Applications/Xcode_9.4.1.app
-      displayName: xcode-select
     - script: pod lib lint
       displayName: pod lib lint
 
 - job: Analyze
   pool:
     vmImage: 'macOS 10.13'
+  variables:
+    DEVELOPER_DIR: /Applications/Xcode_10.1.app
   steps:
-    - script: sudo xcode-select -s /Applications/Xcode_10.1.app
-      displayName: xcode-select
     - script: xcodebuild -scheme Yams clean build-for-testing > xcodebuild.log
       displayName: Generate xcodebuild.log
     - script: HOMEBREW_NO_AUTO_UPDATE=1 brew install --HEAD https://raw.github.com/Homebrew/homebrew-core/master/Formula/swiftlint.rb