Add /_/health endpoint to of-watchdog

[viveksyngh]

Introduce new endpoint /_/health to watchdog for health status of functions which checks for /tmp/.lock file

Added tests for healthHandler

Issues: https://github.com/openfaas/faas/issues/547

Signed-off-by: Vivek Singh vivekkmr45@yahoo.in

Description

Motivation and Context

• [x] I have raised an issue to propose this change (required) Issue raised by Alex: https://github.com/openfaas/faas/issues/547

How Has This Been Tested?

This has been tested on Mac by building the watchdog binary.

curl -i http://localhost:8081/_/health
HTTP/1.1 200 OK
Date: Tue, 03 Apr 2018 03:51:24 GMT
Content-Length: 2
Content-Type: text/plain; charset=utf-8

OK%

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I've read the CONTRIBUTION guide
• [x] I have signed-off my commits with git commit -s
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[alexellis]

I think this looks fine. @johnmccabe can you comment?

[johnmccabe]

Lgtm 👍