provision: add Pelagos support

provision: add Pelagos support

Add provisioning support via Pelagos provisioner
https://github.com/SUSE/pelagos/

Pelagos is pxe boot and provisioning system which created especially
for connecting bare metal nodes to ceph/teuthology testing system.
Integration tests here pelagos/test_pelagos_teuthology/test_pelagos.py
because depends on executed Pelagios service

For enabling pelagos you need add section to teuthology configuration:
    pelagos:
      endpoint: http://your.server.host:5000/
      machine_types: ['type1', 'type2', 'type3']

provision/pelagos.py: added support of Pelagos provisioning project,
                      interface is compatible with FOG provisioner
provision/__init.py: added processing of pelagos section in teuthology
                     configuration and provisioner instantiation
lock/*: added Pelagos provisioner instantiation
nuke/__init__.py: added call to pelagos module for nodes, which are
                   controlled by pelagos, for booting to live images.

Signed-off-by: Roman Grigorev <rgrigorev@suse.de>