BAG prim conflict in CDL export

[boblinchuan]

Originally discussed here in PR 34's comments : link

An issue with CDL export and BAG_prims was identified while developing support for caching static DUTs. @ayan-biswas proposed the following solutions:

1. Put some unique prefixes / suffixes on the BAG_prim cell names when they are being copied into the .cdl netlist. This can be quite difficult to implement.
2. (Better option): include a file with the BAG_prim cell definitions instead of writing it in every file. I think this can solve both the problems, but we need to check.

I agree with the 2nd option. This issue needs some testing.