Parallel processing of the fonts. [DO NOT MERGE]

Font renaming for the SDK is now done in parallel.

This now reduces the running time for this script from about 30 mins to
about 5 to 10 mins. More speedup is expected when fonttools is updated.

Change-Id: I2c405f6d3e637e3067c8a1653e3cae206c32c0c3
(cherry picked from commit c6364fd90de1600526d3431ce0740b6b856e48f0)