Update troubleshooting.asciidoc

[crisdarocha]

Adding "kerberos" to setting. Configuration has changed in 7.x. Needs back porting.

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[elasticmachine]

Pinging @elastic/es-docs (>docs)

[elasticmachine]

Pinging @elastic/es-security (:Security/Authentication)

[lcawl]

LGTM, thanks!