This change switches to v2 API when querying for cluster status on Alertmanager 0.17.0+.
v1 will soon be removed so this is needed to support future Alertmanager releases
We need to know upstream version to decide which API endpoints we can use, metrics don't change between versions so they allow us to do that without any prior knowlage or assumptions
Internal packages are supported by Go 1.5+, any package in /internal/ dir is only importable from the same repo. This will cleanup main dir a bit and provide better namespace for unsee subpackages
