Fix tests using an unregistered operation

[INFO]      [exec] ____________________________ test_operation_command ____________________________
[INFO]      [exec] server = <nuxeo.client.Nuxeo object at 0x7f8463d0a990>
[INFO]      [exec]     def test_operation_command(server):
[INFO]      [exec]         with pytest.raises(ReadTimeout):
[INFO]      [exec]             server.operations.execute(
[INFO]      [exec]                 command="NuxeoDrive.CreateFile",
[INFO]      [exec]                 parentId="",
[INFO]      [exec]                 check_params=True,
[INFO]      [exec] >               timeout=0.0001,
[INFO]      [exec]             )
[INFO]      [exec] server     = <nuxeo.client.Nuxeo object at 0x7f8463d0a990>
[INFO]      [exec] tests/test_nuxeo.py:183: 
[INFO]      [exec] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
[INFO]      [exec] nuxeo/operations.py:175: in execute
[INFO]      [exec]     self.check_params(command, params)
[INFO]      [exec] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
[INFO]      [exec] self = <nuxeo.operations.API object at 0x7f8463d0a210>
[INFO]      [exec] command = 'NuxeoDrive.CreateFile', params = {'parentId': ''}
[INFO]      [exec]     def check_params(self, command, params):
[INFO]      [exec]         # type: (Text, Dict[Text, Any]) -> None
[INFO]      [exec]         """
[INFO]      [exec]         Check given parameters of the `command` operation.  It will also
[INFO]      [exec]         check for types whenever possible.
[INFO]      [exec]         """
[INFO]      [exec]         operation = self.operations.get(command)
[INFO]      [exec]         if not operation:
[INFO]      [exec] >           raise BadQuery("{!r} is not a registered operation".format(command))
[INFO]      [exec] E           BadQuery: u'NuxeoDrive.CreateFile' is not a registered operation
[INFO]      [exec] command    = 'NuxeoDrive.CreateFile'
[INFO]      [exec] operation  = None
[INFO]      [exec] params     = {'parentId': ''}
[INFO]      [exec] self       = <nuxeo.operations.API object at 0x7f8463d0a210>
[INFO]      [exec] nuxeo/operations.py:104: BadQuery