Redis input enhancement

[burdandrei]

Required for all PRs:

• [V] Sign CLA (if not already signed)
• [V] README.md updated (if adding a new plugin)

master_last_io_seconds_ago added
role tag renamed to replication_role

[burdandrei]

I propose to rename role tag to replication_role, cause now it just overwrites global role tag.
Example - i got environment in AWS with tags "AutoscalingGroup,app,role" meaning server role in application. I got "app=api, role=web", "app=api, role=cache". Chef is adding these tags as global tags. Means if i got couple of cache servers i receive now role=master and role=slave, but it's not what i need.

I think replication_role tag reflects the real redis related role.

[sparrc]

where exactly is your global "role" tag coming from? And would this problem affect other users?

[burdandrei]

My global role is coming from AWS tags,
i think other users are using role tag to tag their instances by role too.

[kuchin]

+1

[l13t]

+1

[sparrc]

please rebase your changes and put a very clear **Breaking Change**: redis input plugin notice in the v1.0 changelog.

[burdandrei]

@sparrc done!