Add flags for exporter http timeout and log level

[phsm]

Hi,
Another pull request to add flags for http timeout for connecting to exporter, and log level.

Warning! do not merge yet, I need your help with "log-level" flag. For some reason it always takes the default value (exporter timeout works)

[svenwltr]

I would prever a verbose|v flag over a log-level flag. In my experience I have always to look up how log levels work for each program, while verbose flags are usable out-of-the box.

What is a possible reason to hide Info levels?

[phsm]

As suggested, added "verbose" flag instad of log-level, which changes loglevel from Info (default) to debug.
Tested both of the new options: invoking via flag, and using env variable.