clocksource option for fio

Adding a clocksource option for fio benchmarks would be useful so that gettimeofday can be selected when there are multiple fio processes running on multiple hosts. Assuming ntp is properly configured, this would make aggregating data much easier than it would be otherwise with independent, relative timestamps.

No file or test is named. Start by locating the fio benchmark entry point and its option handling, then determine how benchmark timestamps are collected across processes and hosts. Done means a clocksource option can select gettimeofday for fio runs and the resulting timestamps support cross-host aggregation.

Written by the indexing model from the issue text.