Log messages from Folly are not reported in memcached.log

As seen when investigating MB-43348, messages (including error messages) reported by Folly are not recorded in the normal memcached.log - they only occur in the babysitter.log:

[ns_server:info,2020-12-17T06:11:57.495-08:00,babysitter_of_ns_1@cb.local:<0.128.0>:ns_port_server:log:224]memcached<0.128.0>: E1217 06:11:57.293220  7184 ThreadPoolExecutor.cpp:100] ThreadPoolExecutor: func threw unhandled St15underflow_error exception: ThrowExceptionUnderflowPolicy current:0 arg:-123

This is due to the fact that Folly uses glog for logging, however we do not configure glog at all hence it uses it's default settings to log to stderr (which babysitter in turn records in babysitter.log).