Keep error message notification after stop

If the notification contains an error message, keep it even after the
service is stopped.

Bug: 149876966
Test: adb shell am start-activity \
    -n com.android.dynsystem/com.android.dynsystem.VerificationActivity \
    -a android.os.image.action.START_INSTALL \
    -d file:///file_does_not_exist
Change-Id: I5fdbcaf5ed28343f53d66b3f02ccb66d3c7920ff