illumos gate

Work by Prakash Surya.

This adds a new test to measure ZIL performance.

- A new DTrace collection script to measure latency, and another to collect stacks of threads scheduled off a cpu for creation of flamegraphs.
- Enhances the io.d collection script to produce histograms
- Adds the ability to induce IO delays with zinject
- Adds a new variable (PERF_NTHREADS_PER_FS) to allow fio threads to be distributed to individual file systems as opposed to all IO going to one, as happens elsewhere.
- Refactoring of do_fio_run