IGNITE-1952 Visorcmd: add a command for reset (clear) of metrics

[Saikat Maitra]

Hi,

I have raised PR[1] for the following jira ticket[2].

Please review and let me know if any changes required.

Regards,
Saikat

[1] https://github.com/apache/ignite/pull/1029
[2] https://issues.apache.org/jira/browse/IGNITE-1952