Add random-netsplits tc, trace improvements

[uwiger]

WIP. Added a random_netsplits test case to the locks_leader_SUITE. It currently fails. I've been working on improving the locks_ttb tracing support, and it now works much better for long-running test cases (dropping the initial trace data and keeping the last 1000 events). A pretty-printed trace with an emacs mode header is generated for each failing test case.

The random_netsplits test case is greatly inspired by the locks-test project by @ten0s but I decided to write my own to achieve better integration into the existing test suite.