add optional target attribute to Summary

- example:
  <Summary message="memcpy in fps" target="10.0" scoreType="higherBetter" unit="fps">491.68865488998546</Summary>

- Each test should set its target performance value with printSummaryWithTarget()
- The function will fail (= test fails) if the result does not meet the target.
- target attribute is optional. There can be a performance test without target,
  and such test will always pass as long as the test finishes in time.

Change-Id: Idd7977020fe3b19c36369882ffe2bfa4994574a5
4 files changed