Disable the caplog fixture by default

[gaborbernat]

When profiling a service that generates logs pytest by default automatically collects all log records. This makes the memory profile not true to real life as all log lines are part of the peak memory usage, though in practice after every log that record would be removed. This feature can be disabled for pytest via -p no:logging. At the very least we should document this under gotcha's or even better provide a marker that does this?