[kokoro python] Get script absolute path

Change-Id: I42a9ccb07b43b7dbf8453206ef3747ce4e62606e
diff --git a/kokoro/kokoro_build.sh b/kokoro/kokoro_build.sh
index 6abadc9..38ff116 100755
--- a/kokoro/kokoro_build.sh
+++ b/kokoro/kokoro_build.sh
@@ -7,7 +7,7 @@
 OUT="${KOKORO_ARTIFACTS_DIR}/out"
 PYTHON_SRC=${KOKORO_ARTIFACTS_DIR}/git/cpython3
 
-BASEDIR=$(dirname "$0")
+BASEDIR="$( cd "$(dirname "$0")" >/dev/null 2>&1 ; pwd -P )"
 if [ "$(uname)" == "Darwin" ]; then
     # http://g3doc/devtools/kokoro/g3doc/userdocs/macos/selecting_xcode
     sudo xcode-select -s /Applications/Xcode_12.2.app/Contents/Developer