tools/utils: create utils module to unify test results

This patch introduces `utils.py` in the tools directory, unifying
test result handling. It includes a `banner` function to create
consistent test output headers and a `Results` class for logging
the output of the different scripts.

Signed-off-by: Leandro Belli <leandro.belli@arm.com>
Change-Id: Ia5d49ce4b34ea0f4f5c6d0b1d43090f6da75906a