When Vault is concurrently creating and revoking leases for MongoDB
users as part of the database secrets engine, and then loses connection
to MongoDB, it can panic. This occurrs because the RevokeUser path does
_not_ lock the mutex, but the CreateUser path does. Both threads of
execution can concurently decide to call c.session.Close() in
mongodb/connection_producer.go:119, and then mgo panics when the second
close attempt occurs.

* Add ability to configure the NotBefore property of certificates in role api

* Update index.html.md

* converting field to time.Duration

* setting default back to 30s

* renaming the parameter not_before_duration to differentiate between the NotBefore datetime on the cert

* Update description

* re-add performancestandycode for health api call

* update debounce timeout for namespace input on the auth page

* re-fetch cluster model on successful init

* 500ms for the debounce

* swap auth methods after successful api call so that the auth box doesn't jump around

* move list capability fetch to namespace component and don't use computed queryRecord to fetch it

* convert ed models to JSON so that they're unaffected by store unloading

* serialize with the id for the auth method models

* speed tests back up with different polling while loop

* login flash isn't in the same run loop so no longer needs withFlash

* Allow specifying role-default TTLs in AWS secret engine

* Add an acceptance test

* Add docs for AWS secret role-default TTLs

* Rename default_ttl to default_sts_ttl

* Return default_ttl as int64 instead of time.Duration

* Fix broken tests

The merge of #5383 broke the tests due to some changes in the test style
that didn't actually cause a git merge conflict. This updates the tests
to the new style.

* fix token expiration calculation

* move authenticate to an ember concurrency task

* don't show logged in nav while still on the auth route

* move current tests to integration folder, add unit test for expiration calculation

* fix auth form tests

This might be a typo, It says `A user may have a client token sent to her` instead it should say `A user may have a client token sent to them`

Minor grammar fix.

* The added method customTLSDial() creates a tls connection to the zookeeper backend when 'tls_enabled' is set to true in config

* Update to the document for TLS configuration that is  required to enable TLS connection to Zookeeper backend

* Minor formatting update

* Minor update to the description for example config

* As per review comments from @kenbreeman, additional property description indicating support for multiple Root CAs in a single file has been added

* minor formatting