Configuration and various fixes

Added

• Configuration mechanism via file and CLI flags (#91)
• SBD devices total count metric ha_cluster_sbd_devices_total (#92)

Changed

• BC break: rename some labels to make aggregated promql queries possible (#94)

Fixed

• Paths to external tools are no longer hardcoded (#87)
• BC break: ha_cluster_pacemaker_config_last_change now uses its value as the last config timestamp, rather than its timestamp itself (#89)
• ha_cluster_drbd_connections_sync number format (#86)

RPMs

https://build.opensuse.org/package/show/server:monitoring/prometheus-ha_cluster_exporter?rev=18