Fixed rfxtrx binary sensor missing optional keyerror data_bits

[basschipper]

Description:

Fixed rfxtrx binary sensor missing optional keyerror data_bits

2018-02-28 11:24:30 ERROR (MainThread) [homeassistant.components.binary_sensor] Error while setting up platform rfxtrx
Traceback (most recent call last):
  File "/usr/src/app/homeassistant/helpers/entity_platform.py", line 84, in async_setup
    SLOW_SETUP_MAX_WAIT, loop=hass.loop)
  File "/usr/local/lib/python3.6/asyncio/tasks.py", line 358, in wait_for
    return fut.result()
  File "/usr/local/lib/python3.6/asyncio/futures.py", line 243, in result
    raise self._exception
  File "/usr/local/lib/python3.6/concurrent/futures/thread.py", line 56, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/usr/src/app/homeassistant/components/binary_sensor/rfxtrx.py", line 58, in setup_platform
    if entity[CONF_DATA_BITS] is not None:
KeyError: 'data_bits' 

Related issue (if applicable): fixes #12776

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.github.io#<home-assistant.github.io PR number goes here>

Example entry for configuration.yaml (if applicable):

binary_sensor:
  - platform: rfxtrx
    devices:
      0b110001008744e10a000070:
        name: Mailbox
        device_class: opening

Checklist:

• The code change is tested and works locally.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.github.io

If the code communicates with devices, web services, or third-party tools:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies are only imported inside functions that use them (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[basschipper]

Fixes #12776 / #12688, probably introduced by #12463.

[balloob]

Thanks! Sorry about introducing the issue 🤔 Will make it part of the next hotfix 🎉