[TEST] Disable translog flush in CorruptedTranslogTests
[TEST] more debugging for GeoBoundsTests
Internal: make sure that the request context is always copied from REST to transport layer

Also renamed HeadersCopyClientTests since it tests a class that was renamed and removed randomization around client wrapper, as it now needs to be weapped all the time to copy the context, doesn't depend on useful headers that have been registered anymore.

Relates to #7610
[TEST] use local random instance rather than thread local version

This influences reprocucibility dramatically since it modifies the
test random sequence while it should just use the private random
instance.