print output to JSON_OUTPUT_PATH

[veictry]

NVBUG: http://nvbugs/200772213

if we define JSON_OUTPUT_PATH, the script will print output to $JSON_OUTPUT_PATH with JSON format
VRL can load the output from this file and print the content with VRL format

<subtest start time>
&&&& RUNNING <test name>
<test log>
&&&& LIT RESULT <lit test status>
&&&& EXPECTING <expected result>, GOT <the real result>
&&&& <test status/code> <test name>
<subtest end time>

• see test result here:
  DVS-SC link: http://scbuilds4u.nvidia.com/dvs/#/change/3086522139432407.7?showTab=DVS
  test link: http://scvrlweb.nvidia.com/showjob.php?job=8156440
• if not define JSON_OUTPUT_PATH:
  DVS-SC link: http://scbuilds4u.nvidia.com/dvs/#/change/3086522139432407.6?showTab=DVS

  failed because the pattern "&&&& RUNNING... &&&& PASS..." can not be found
  test link: http://scvrlweb.nvidia.com/showjob.php?job=8156414

the full codes: https://p4sw-swarm.nvidia.com/changes/30715467

[wmaxey]

I've resolved the conflicts in this patch. I'll begin another round of CI tonight on AUS-DVS to make sure the normal path still functions. I'll commit this weekend.