keydb multimaster support

[mihaiush]

Add support for info keys like master_[0-9]_ which are produced by keydb in case there are more than 1 master.

redis_master_link_up{master_host="m0.server.local",master_port="6377"} 1
redis_master_link_up{master_host="m1.server.local",master_port="6377"} 1

[oliver006]

Thanks for the PR! Looks good but a couple of smaller issues:

• There are a couple of comments in the linter that make sense (see here: https://cloud.drone.io/oliver006/redis_exporter/1709/1/15)

• Can you also please run "go fmt" on your change to make sure it's properly formatted?

[coveralls]

Pull Request Test Coverage Report for Build 1724

• 10 of 10 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 92.167%

---

Totals
Change from base Build 1700:	0.02%
Covered Lines:	1812
Relevant Lines:	1966

---

💛 - Coveralls

[codecov]

Codecov Report

Merging #710 (340aeec) into master (8deeeaf) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #710      +/-   ##
==========================================
+ Coverage   88.24%   88.26%   +0.02%     
==========================================
  Files          16       16              
  Lines        1956     1960       +4     
==========================================
+ Hits         1726     1730       +4     
  Misses        154      154              
  Partials       76       76              

Impacted Files	Coverage Δ
exporter/info.go	95.93% <100.00%> (+0.04%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[oliver006]

Looks good, thanks for the changes. Two minor issues and then this should be good to go!