IMPALA-1513: Reduce contention in periodic counter updater

In order to reduce the lock contention in the periodic counter updater,
this patch substitutes the single pthread_mutex lock that what being used with
four spinlocks, each of which protects updates to a different category of
counters this periodic updater maintains.

Change-Id: I655770586ee297fba4bed8e9c65b3e9734f4a298
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5384
Reviewed-by: Ippokratis Pandis <ipandis@cloudera.com>
Tested-by: jenkins