vppapigen: make json in parallel

Type: improvement

This patches makes the make json-api-files
run in parallel in the same python runtime.

Default number of workers is 8, and run time
goes from ~20s to ~2s on average.

Change-Id: Id8cff013889db2671f6b6b4af9a019460c656f81
Signed-off-by: Nathan Skrzypczak <nathan.skrzypczak@gmail.com>
diff --git a/src/tools/vppapigen/vppapigen_crc.py b/src/tools/vppapigen/vppapigen_crc.py
index 525f6c0..f7e8296 100644
--- a/src/tools/vppapigen/vppapigen_crc.py
+++ b/src/tools/vppapigen/vppapigen_crc.py
@@ -7,7 +7,7 @@
 #
 # Plugin entry point
 #
-def run(args, input_filename, s):
+def run(output_dir, input_filename, s):
     j = {}
     major = 0
     minor = 0