[CI][VSTS] Ensure that the required simulators are present in the machine. (#10486)

tools/devops/automation/templates/build/build.yml

@@ -99,6 +99,12 @@ steps:
     provisioning_extra_args: '-vvvv'
   timeoutInMinutes: 250
 
+- bash: |
+    set -x
+    set -e
+    $(Build.SourcesDirectory)/xamarin-macios/system-dependencies.sh --provision-simulators
+  displayName: 'Provision simulators'
+
 - bash: |
     set -x
     sudo rm -Rf /Developer/MonoTouch