Fix instance and object name in performance counters with backslashes

[vlastahajek]

closes #4499

Overview

replaced complex regexp marching with simple index searching
Added unit test for counterPath parsing

Required for all PRs:

• Signed CLA.
• Has appropriate unit tests.

[danielnelson]

@jedthe3rd Could you test this fix with your setup? telegraf-1.8.0~9f9bd961_windows_amd64.zip

[vlastahajek]

I realized that there can be even more complex counter paths, e.g. \\host\object(d:\f\I(a)x)\counter(d:\f(d)\i).
I haven't found any restrictions of counter name, instance name or object name. I tested that complex path on Windows performance counters API function PdhParseCounterPathW and as it was able to parse it, I find such complex path valid.
So I have created better, more bulletproof, parser. It's ~6x slower than previous, but still a lot faster than regexp.
Unit test has been a lot more extended as well.

[danielnelson]

@jedthe3rd Here is an updated build with the latest fixes for testing, if you are available to verify we can add this for 1.7.4:

• telegraf-1.8.0~1789ce0b_windows_amd64.zip

[vlastahajek]

I"m sorry for discontinuous commits. The latest one is just an improved unit test.