Canonicalize XML strings before comparing to reduce flakiness. am: 974286e087 am: e0f3789531 am: bf4df6abbf

Original change: https://android-review.googlesource.com/c/platform/tools/treble/+/1681545

Change-Id: I26f09446e5cd5c11c1fd50a5e12de8033c17c47f