brillo: Add util and ab flow posix test harness.

Setup a test harness for ab flow in a posix environment. Utility functions and
ab flow logic, which will be used in a uefi environment, can be tested
by adding unit tests to

TEST=Passing unit tests for utf8 to ucs2 conversion and ongoing ab flow
logic testing.

Change-Id: Ifd3591e4cd54d92ef4979c9f4cc5df69359b96bd
6 files changed