releasetools: build_super_image.py should unpack */build.prop

build_super_image.py attempts to retrieve the "ro.product.device"
property, which requires parsing the */build.prop files from the target
files package. This fixes the following error:
"ExternalError: couldn't resolve ro.product.device"

Test: ./otatools/releasetools/build_super_image.py -p ./otatools
aosp_arm64-target_files.zip super.img

Change-Id: I592524a27b1a4e7544644b1a344071cff9718942
diff --git a/tools/releasetools/build_super_image.py b/tools/releasetools/build_super_image.py
index 38ea3d6..99c0563 100755
--- a/tools/releasetools/build_super_image.py
+++ b/tools/releasetools/build_super_image.py
@@ -55,7 +55,7 @@
 logger = logging.getLogger(__name__)
 
 
-UNZIP_PATTERN = ["IMAGES/*", "META/*"]
+UNZIP_PATTERN = ["IMAGES/*", "META/*", "*/build.prop"]
 
 
 def GetPartitionSizeFromImage(img):