improved logging of new_concurrency_throttle:change_tokens
improved logging of new_concurrency_throttle:change_tokens

This is not so trivial code and not perf-sensitive. So verbose logging
should be a must.

Change-Id: I1e50cbc078f86b35fd08ea1688113a41781fb19b
Reviewed-on: http://review.couchbase.org/39471
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>

t3rm1n4l/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,nimishzynga/ns_server,mschoch/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,nimishzynga/ns_server,membase/ns_server,membase/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,membase/ns_server,mschoch/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,membase/ns_server,mschoch/ns_server,mschoch/ns_server,ceejatec/ns_server,nimishzynga/ns_server,ceejatec/ns_server,nimishzynga/ns_server,mschoch/ns_server,nimishzynga/ns_server,nimishzynga/ns_server