Add post-start check for logstash ingestors using syslog.

[bengerman13]

We're using these post-checks essentially to fail a deployment if it leaves the cluster in a bad state, and thought others might like to make use of them. We have them defaulted to on, but I'd be happy to reverse the default if that helps get this merged.

[CLAassistant]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[bengerman13]

I signed the CLA, but it still shows as needing to be signed. Does that mean @wjwoodson needs to sign it, too?

[bengerman13]

@wjwoodson I think we confirmed in another PR that the issue here is we need you to sign the CLA if you're willing.

[axelaris]

Hi @bengerman13, thank you for contribution! Could you please check my comments in the code?

[bengerman13]

Thanks for looking @axelaris. I responded to one of the comments.

I think we're stuck until @wjwoodson can sign the CLA, so no rush here :)

[axelaris]

We disabled CLA eventually, so no worries. Could you please also rebase your PR to include bpm?

[siennathesane]

@bengerman13 bump

[axelaris]

LGTM

[axelaris]

Thank you @bengerman13 !