Hotfix/proxy root instance

Please both @alain.takoudjou and @rafael to review before merging.

First commit fixes the code for "getRootPartition" Second commit renames requested slappartitions to use existing test partitions. To be more specific: self.add_free_partition(2) creates following partitions (dump taken at the end of one test) hence the renaming.

({'computer_reference': 'computer',
  'connection_xml': None,
  'partition_reference': 'MyFirstInstance',
  'reference': 'slappart0',
  'requested_by': 'slappart2',
  'requested_state': 'started',
  'slap_state': 'busy',
  'slave_instance_list': None,
  'software_release': 'http://sr//',
  'software_type': 'default',
  'xml': "<?xml version='1.0' encoding='utf-8'?>\n<instance/>\n"},
 {'computer_reference': 'computer',
  'connection_xml': None,
  'partition_reference': None,
  'reference': 'slappart1',
  'requested_by': None,
  'requested_state': 'started',
  'slap_state': 'free',
  'slave_instance_list': None,
  'software_release': None,
  'software_type': None,
  'xml': None})

Is the renaming correct?