create_tenants fails when tenant and domain have fields with same name

[nschlemm]

e.g. when both tenant and domain model have a "status" field, this will throw:

Traceback (most recent call last):
  File "manage.py", line 15, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python3.6/site-packages/django/core/management/__init__.p
y", line 371, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python3.6/site-packages/django/core/management/__init__.p
y", line 365, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python3.6/site-packages/django/core/management/base.py",
line 280, in run_from_argv
    parser = self.create_parser(argv[0], argv[1])
  File "/usr/local/lib/python3.6/site-packages/django/core/management/base.py",
line 254, in create_parser
    self.add_arguments(parser)
  File "/usr/local/lib/python3.6/site-packages/django_tenants/management/command
s/create_tenant.py", line 31, in add_arguments
    parser.add_argument('--%s' % field.name, help="Specifies the %s for the tena
nt's domain." % field.name)
  File "/usr/local/lib/python3.6/argparse.py", line 1348, in add_argument
    return self._add_action(action)
  File "/usr/local/lib/python3.6/argparse.py", line 1711, in _add_action
    self._optionals._add_action(action)
  File "/usr/local/lib/python3.6/argparse.py", line 1552, in _add_action
    action = super(_ArgumentGroup, self)._add_action(action)
  File "/usr/local/lib/python3.6/argparse.py", line 1362, in _add_action
    self._check_conflict(action)
  File "/usr/local/lib/python3.6/argparse.py", line 1501, in _check_conflict
    conflict_handler(action, confl_optionals)
  File "/usr/local/lib/python3.6/argparse.py", line 1510, in _handle_conflict_er
ror
    raise ArgumentError(action, message % conflict_string)
argparse.ArgumentError: argument --status: conflicting option string: --status

I'll propose a simple "--domain-" prefix for those automatically added fields