skpbench: skiaperf.py modifications

- Appends the clock and unit to the result type (e.g. "accum_cpu_ms").
- Removes the "options" key.
- Adds "bench_type" and "source_type" keys to the properties.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4737

Change-Id: I2fd27eac4f42f443131fef6b1774f20e60571cd5
Reviewed-on: https://skia-review.googlesource.com/4737
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>