Prepare iOS device for build+test recipe

Change-Id: I6a5755918343bea772ac7e991aa563f1a79e1e72
Bug: https://github.com/flutter/flutter/issues/142917
CP Request: https://github.com/flutter/flutter/issues/143326
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/54841
Commit-Queue: Keyong Han <keyonghan@google.com>
Reviewed-by: Victoria Ashworth <vashworth@google.com>
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/55082
Reviewed-by: Casey Hillers <chillers@google.com>
Commit-Queue: Victoria Ashworth <vashworth@google.com>
Reviewed-by: Keyong Han <keyonghan@google.com>