Fix kibana password

[joerg]

Do not use, or better misuse, run_state in this case. It does not work this way, so better just use attribute?
This also fixes Issue #55.

[joerg]

I have no experience so far with Jenkins and this build failure, but it seems that this error is completely unrelated to my pull request...

[martinb3]

@joerg I'm going to move this into #102. Just for some background:

Elkstack is designed to treat Kibana credentials as data not truly owned by the stack. Many users will end up putting nginx configurations that protect Kibana with ldap, htaccess, SAML, etc, and elkstack is intended to remain agnostic about those decisions. node.run_state is intended for transient data, so elkstack expects wrapper cookbooks to own the credentials data, but pass it to elkstack via node.run_state as transient data. Elkstack guarantees it won't persist that data anywhere -- the responsibility lies on the wrapper cookbooks for that.