Correctly deinit logging before reinit when changed on the fly

[graydon]

When we set the log level on the fly with, say, an http command ll?partition=tx&level=trace, we update a basic per-partition table and then (re)initialize the rest of the tracing subsystem. Unfortunately this only works correctly if we deinitialize the logging subsystem before reinitializing it (as we do most places where dynamic tracing reconfiguration are allowed). In this one path we fail to deinit before reinit, and this ultimately means the max log level never gets propagated over the rust bridge, and the new tracing facility on the rust side never activates.

(It does activate already if you set the initial log level to trace, just not if you reconfigure on the fly)

Anyway, this change fixes the reconfiguration path to deinit before reinit.

[MonsieurNicolas]

r+ 571083c