Fix lit/example/many-tests pickling issue

Summary:
The multiprocess module uses pickling to transfer
information between processes and does not know how to pickle
the class created in the lit.cfg file and thus the example
fails.

Implement ManyTests in a separate file and import for the
example test passes

Patch by Nathan Lanza <nathan@lanza.io>

Differential Revision: https://reviews.llvm.org/D51328

llvm-svn: 342269