have build_test.bash work when run as ./build_test.bash

Test: ./build_test.bash
Bug: 67478260

Change-Id: I027dcf7505def2253b9e41721aa6c226239f69c7
diff --git a/build_test.bash b/build_test.bash
index 065d7f6..6edaa66 100755
--- a/build_test.bash
+++ b/build_test.bash
@@ -28,6 +28,7 @@
 export TRACE_BEGIN_SOONG=$(date +%s%N)
 
 export TOP=$(cd $(dirname ${BASH_SOURCE[0]})/../..; PWD= /bin/pwd)
+cd "${TOP}"
 source "${TOP}/build/soong/scripts/microfactory.bash"
 
 case $(uname) in