Add X-Duration-Seconds header for HTTP mode

Changelog:

• Add X-Duration-Seconds for HTTP mode via b899713

Don't follow redirects

Allows redirects from function to be passed back to the calling code.

Implement graceful shutdown as per classic watchdog 0.9.4

Changelog:

• Implement graceful shutdown as per classic watchdog 0.9.4 #28

This creates a delay between SIGTERM and shutting off new HTTP connections meaning the Kubelet has a chance to remove the watchdog from the pool of HTTP endpoints it is using.

Add /_/health/ endpoint

Changelog:

• Enables HTTP health-checks via route: /_/health/

Pass HTTP Path upstream

Changelog:

• Pass HTTP Path upstream #21

Pass HTTP Host header

The HTTP Host Header was not being passed through to the function template. Includes: #24

HTTP mode enhancement

Closes the request body if supplied to prevent dangling connections.

Pass QueryString to upstream_url in HTTP Mode

Fixes:

• HTTP mode - Pass QueryString along to upstream_url #18 via 7805183 @alexellis

Add exec_timeout for HTTP mode

• Adds exec_timeout for HTTP mode

HTTP KeepAlive tuning

Tunes internal upstream HTTP connection with KeepAlive