Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "prototypes: bifrost: Remove OPNFV specific group_vars file"
  - prototypes: bifrost: Remove OPNFV specific group_vars file

    The only reason we had this file was because we had to define our own
    'ssh_public_key_path' variable to look in the /root directory since we
    were running everything as root. Since we are now moving away from this
    approach, this file is not needed anymore.

    Change-Id: Ic938c4c8c877c95ce261721dc32fc5147081e236
    Signed-off-by: Markos Chandras <mchandras@suse.de>