compat/utils: Add copy of python multiprocessing pool for pre 2.7.3 issues

python 2.7 shows hangs with issues in its pool implmenetation. Rather than
try and hack around these, add a copy of the working pool implementation
to the compat module from 2.7.3.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>