Fix ota test case

It was failing with:
build/make/core/main.mk:2: Calling make directly is no longer supported.
build/make/core/main.mk:3: Either use 'envsetup.sh; m' or 'build/soong/soong_ui.bash --make-mode'
build/make/core/main.mk:4: *** done.  Stop.

Test: system/core/bootstat/boot_reason_test.sh ota
Change-Id: I4fea25f1c09e6ec2f346b6de3749699e254ffd26
diff --git a/bootstat/boot_reason_test.sh b/bootstat/boot_reason_test.sh
index 8979b0c..f379d76 100755
--- a/bootstat/boot_reason_test.sh
+++ b/bootstat/boot_reason_test.sh
@@ -636,7 +636,7 @@
   rm -r ${ANDROID_PRODUCT_OUT}/obj/ETC/system_build_prop_intermediates ||
     true
   pushd ${ANDROID_BUILD_TOP} >&2
-  make -j50 >&2
+  build/soong/soong_ui.bash --make-mode >&2
   if [ ${?} != 0 ]; then
     popd >&2
     return 1