Usernames needs to be lowercase in foreman.

This may not be needed because of

http://projects.theforeman.org/issues/4439

but just in case, make hte hidden user be lowercase when created.
Index the content when the syncing finishes
Index only when synchronization not handled by Dynflow action

The Actions::Katello::Repository::Sync itself handled then indexing of
the content: no need to do it again the after_sync callback.
Fix indexing after scheduled tasks

Wrong class caused task.progress to return hash that doesn't have
error_details method.
Merge pull request #3785 from iNecas/index-content-after-sync

Index the content when the syncing finishes
Require foreman-tasks ~> 0.3.6

We need it for `for_action` and `for_resource` scope definitions
Merge pull request #3736 from bkearney/bkearney/downcase-usernames

Usernames needs to be lowercase in foreman.
Merge pull request #3791 from iNecas/foreman-tasks-bump

Require foreman-tasks ~> 0.3.6