Fix potential memory leak in exporter by closing HTTP response body

Changelog for 0.27.6:

Commits
b22cb63 Update error handling for empty metrics responses in exporter by @alexellis
667577f Remember to close HTTP body from response by @alexellis
8d5dcdf CE 60 day limit is only for evaluation purposes by @alexellis
609b43b Introduce EULA for OpenFaaS CE by @alexellis
1ab3f32 Prepare OpenFaaS editions for telemetry data collection by @alexellis

Changes: 0.27.5...0.27.6

Generated by Derek