Add the ability to connect to multiple Cloud Foundry datasource bindi…

[ihrigb]

…ngs.

This needs to be enabled via --use-cf-bindings.

[coveralls]

Coverage decreased (-38.5%) to 15.608% when pulling 8266c20 on ihrigb:dev/cf into 6e3d130 on wrouesnel:master.

[coveralls]

Coverage decreased (-1.1%) to 53.039% when pulling a09098c on ihrigb:dev/cf into 6e3d130 on wrouesnel:master.

[wrouesnel]

This is a fairly significant change which I need to figure out the ramifications of. It's flirting pretty closely to adding blackbox_exporter style support, where Prometheus would instead hit a /probe endpoint and send the relevant polling details.