The default is nolog, which prevents the unit tests in
the main pkg from being active, since otherwise they
would print as if they were being run like a dev build
of the daemon. Users can pass in custom tags when running
the Makefile by passing arguments using the log variable,
e.g. log="xxxxx xxx"".
This commit makes sure old log files are deleted before running the
integration tests. Previously new logs would be added to the existing
ones, causing a big mess. This was especially messy during flake
hunting, as all logs would be kept.
In addition, we now print the date before every start of the integration
tests, which is useful to see how long they have been running, for
instance in case of a deadlock.
