prometheus best practices, TLS and basic auth support

[yeoldegrove]

The main point was to enable TLS support.
One pre-requisite for this was a log.Logger object (reference) which is not available in the currently used logging package logrus.
I took this as an opportunity to port some best practices from e.g. HAProxy exporter and MySQL Server exporter. This includes:

• using promlog instead of logrus for logging a38c72a
  • DEPREACTION: log format changed due to this
• using kingpin instead if pflag to parse commandline a38c72a
  • this is completely backwards compatible for the config file and command line argument setup
    • some flags are marked as deprecated but will still work
  • includes a wrapper to parse viper config and overwrite it with kinpin flags
• add TLS and basic auth support by using exporter-toolkit
• build binaries with promu 945cbc1
• test: build, run and test binary 3017a2f

In addition to that, the OBS + release CI is kind of broken at the moment. These commits tend to fix it:

• fix github url in specfile e219a02
• fix github release e08c01a

[stefanotorresi]

Some questions inline just to remind myself, let's have a chat face to face to discuss some of the more extensive changes.

[yeoldegrove]

@stefanotorresi force pushed the changes you wanted. It is ready to merged from my point of view.