Feature: new data transfer servers

[pneerincx]

• New data_transfer server inventory group:
  • Renamed data_staging inventory group to data_transfer group to prevent confusion with the Slurm Data Staging QoS level and corresponding Slurm ds nodes.
  • Added data transfer server to inventory for Nibbler.
  • Removed data transfer server from inventory for Talos.
  • deploy-os_servers.yml: Added code to create related OpenStack components.
  • Added data_transfer inventory group to several single role playbooks.
  • Added data_transfer inventory group to roles/regular_users/tasks/main.yml.
  • Moved filtering of users/groups that should not be allowed access at all or that should receive only data transfer capabilities from ssh-ldap-wrapper in ldap role to sshd_config in sshd role.
  • Updated mount_volume role to create group folders in /groups on data transfer servers.
  • Added mount_volume role to single role playbook for data transfer servers.
  • Updated logins role: Added login check script to create chrooted fake homes for users in the data_transfer_only_group.
  • Added data_transfer_only_group variable for Gearshift, Talos and Nibbler.
  • Updated sshd role to use data_transfer_only_group variable and use ForceCommand directives to allow only sftp on port 22 and rsync on port 443 on data transfer servers.
  • Updated rsyncd role: added separate configs for regular users versus users in the data_transfer_only_group group. Removed module for regular home dirs as they are not needed for data transfers.
• Collateral fixes / improvements:
  • Fixed comment in dynamic inventory.
  • online_docs role: Replaced very long lists of hostnames in templates with a variable in roles/online_docs/defaults/main.yml.
  • Added "connection: local" to make tasks work with static inventories too.
  • Updated mount_volume role: Added support for multiple volumes as opposed to a single one and removed machine specific logic from role: differences between machines are now completely handled by group_vars.