Fix fwatchdog timer memory leak issue
Fix fwatchdog timer memory leak issue

Use timer.AfterFunc to make sure goroutine could be gc.

Signed-off-by: Mike Chiu <faf110d6590800f7cada9ee8f95954700d94e728@pentium.network>

alexellis/faas,alexellis/faas,rgee0/faas,rgee0/faas,rgee0/faas,alexellis/faas,alexellis/faas,rgee0/faas,rgee0/faas,alexellis/faas,rgee0/faas,rgee0/faas,openfaas/faas,rgee0/faas,alexellis/faas,rgee0/faas,rgee0/faas,openfaas/faas,alexellis/faas,alexellis/faas,openfaas/faas,alexellis/faas