[SCHEMA CHANGE] Shorten uuids to 88 bits.

Currently the uuid's exposed to the world by Flow are 128 bit hex uuids.
This patch converts the internal storage of uuids from 128 bits to 88
bits.  Flow's use case builds a low enough number of uuids/second that
88 bits is still sufficient to ensure statistically significant
uniqueness.

Additionally a followup patch switches the external representation of
UUID's from hexadecimal to alphadecimal(base 16 to base 36).  The
combination of shortening and changing base provides a final result of
all displayed UUID's being half of their previous length.

These two patches have full backwards compatibility with base 16 and 128
bit uuids.

(cherry picked from commit 8bff86882c0dac9c4ed7d784a772ae93e4f24411)

Change-Id: If2152c608e525913ee6f28d3760d1da4c04ce778