Add test name to e2e cluster members

[tjungblu]

This should aid in debugging test flakes, especially in tests where the process is restarted very often and thus changes its pid. Now it's a lot easier to grep for different members, also when different tests fail at the same time. The test TestDowngradeUpgradeClusterOf3 as mentioned in #13167 is a good example for that.

Signed-off-by: Thomas Jungblut [email protected]