Path to beta release

Problem/Motivation

There's lot of RTBC patches which is hard to order for real project
No testing automation is setup for 8.x-3.x branch

Proposed resolution

Reworks tests out of simpletest dependency and make them pass
Build a list of "must have" and "could have" issues (somehow ordered)
Assign this issue to this one as parent
Get the issues commited

Remaining tasks

Must have
#3067225: Missed samlauth.authentication:idp_entity_id config schema
#3087233: Ignore e-mail synchronization if user_mail_attribute is empty
#3086441: Invalid response, status: InvalidNameIDPolicy
#2848809: Login/logout fails with non-default language being active with the URL prefix negotiation
#3064958: Drupal\Core\Entity\EntityStorageException: Constant ONELOGIN_CUSTOMPATH already defined Assigned to: moshe weitzman

Could have
#2913308: RelayState set to self (login/logout) not recognized on multilingual sites
#3070321: Token in Service Provider Configuration usage
#2925171: Use externalauth::register event vs hook_user_presave

User interface changes

could be

API changes

could be but with BC shim

Data model changes

some extra config options with BC upgrades

Release notes snippet