Service Dialog Element Type tests

I think a happy medium would be this:
```python
    def element_type(self):
        if self.choose_type in ("Drop Down List", "Radio Button"):
            entry_table.click_cell(header='value', value='<New Entry>')
            fill(element_form, {'entry_value': self.entry_value,
                                'entry_description': self.entry_desc})
        elif self.choose_type == "Text Area Box":
            text_area_table.click_cell(1, value=self.text_area)
        else:
            # TypeError is not the best exception for this,
            # so find or create something in cfme_tests.exceptions
            raise TypeError('Unknown service dialog element type: %s' % self.choose_type)
```

Switched to if/elif so we aren't checking `choose_type` if it matches in the first step, then added the else clause to raise the unknown element type exception.