added missing handcar_cosim.so file

Created by: Leo-Wang-JL

Signed-off-by: Jingliang Wang jwang1@futurewei.com

The handcar_cosim.so was intended to be included in the initial commit but it was omitted unintentionally due to a .gitignore file.

The handcar_cosim.so can be also build from the code in the handcar directory. However we found that there are some files missing in that directory as well. We will get that addresses ASAP so that a user can confidently build the handcar_cosim.so oneself.