Produce benchmark JSON schema v2

- No more '(Display)' strings in the GPU names, but store devices as
  `{'name': name, 'type': 'CPU/CUDA/OPENCL', 'is_display': bool}`
- Introduces testing with py.test & pipenv. The test suite is far from
  complete, though.

benchmark/farm.py

@@ -11,6 +11,8 @@ import tempfile
 SCRIPT_PATH = os.path.realpath(__file__)
 SCRIPT_DIR = os.path.dirname(SCRIPT_PATH)
 
+RESULT_JSON_SCHEMA_VERSION = 2
+
 import foundation
 from foundation import (benchrunner,
                         buildbot,
@@ -286,8 +288,10 @@ def ensureImageOutputDir(results_output_dir):
 
 
 def getResultJSONString(ctx, results):
+    import copy
     # Convert custom classes to dictionaries for easier JSON dump.
-    json_results = results
+    json_results = copy.deepcopy(results)
+    json_results['schema_version'] = RESULT_JSON_SCHEMA_VERSION
     stats = json_results['stats']
     for scene in ctx.scenes:
         if scene not in stats: