Adding output plugin for Splunk

[tmartin14]

Required for all PRs:

• Signed CLA.
• Associated README.md updated.
• Has appropriate unit tests.

This output plugin will forward enable forwarding of metrics to Splunk.

[danielnelson]

closes #3176

[tmartin14]

would love to get a little help here. The circleci tests continue to FAIL for a number of plugins. Is this normal?

Also, for this particular output plugin, I am getting the following error:
--- FAIL: TestSplunk (0.00s)
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x28 pc=0x71356e]

Is there any known solution for this?

Any assistance would be greatly appreciated.

[danielnelson]

Can you rebase or merge master? There have been a lot of changes since you branched.

[tmartin14]

I got everything worked out, but yes I can rebase and pull down the latest master. I'll close this PR and open a new one when I get to that point.

[tmartin14]

Updated with new pull request: #4185