Previously a DebugLogger was used when probe tests ran 'custom
daemons', which provided a means to inspect captured logs but logged
to console. This patch replaces that DebugLogger with a 'normal' swift
logger that is adapted to also capture logs and support log
inspection.
Change-Id: I25da3aa81018c5de7b63e5584ac6a9dbb73243db
Move DebugLogger and associated classes to its own module under test
so that it can be imported (for example in probe tests) without
requiring all the dependencies in test/unit/__init__.py.
Change-Id: I0ea3c26e54d91f27159805a45e49ad7f8f0e0431