Change art script to use exec

Change-Id: I0ae2a7e35ba4bc2675836b45677aa535eccf0850
diff --git a/tools/art b/tools/art
index 6af2151..c3fe0f5 100755
--- a/tools/art
+++ b/tools/art
@@ -38,6 +38,6 @@
 ANDROID_DATA=/tmp/android-data\
  ANDROID_ROOT=$ANDROID_HOST_OUT\
  LD_LIBRARY_PATH=$ANDROID_HOST_OUT/lib\
- $invoke_with $ANDROID_HOST_OUT/bin/$oatexec\
+ exec $invoke_with $ANDROID_HOST_OUT/bin/$oatexec\
  -Ximage:$ANDROID_HOST_OUT/framework/core.art \
  $*