memcached logs always use Z (UTC) for timezone when logging

It looks like some recent changes in the memcached logging has caused the timezone in the memcached logs to be always printed with Z, referring to UTC, even when the timezone of the system (and other logs) is different.

Looks like the "Z" is hard coded here https://github.com/couchbase/kv_engine/blob/master/logger/spdlogger.cc#L44

Note the time is not actually converted to UTC, it is still using the system's local timezone. This is misleading as the reader may (quite reasonably) think the log message refers to UTC and hence struggle to correlate log messages.