Parameters For All Drivers and Base Connection Do Not Support Tuple Lists

Currently the parameters argument to the base connection's request method is required to be a dict.

This prevents passing multiple query-string arguments with the same key.

The code sometimes works 'as is' because urlencode supports either dicts/tuple lists, but throughout the libcloud codebase there is code like:

EC2Connection:

def add_default_params(self, params):
params['SignatureVersion'] = '2'
params['SignatureMethod'] = 'HmacSHA256'
params['AWSAccessKeyId'] = self.user_id
params['Version'] = API_VERSION
params['Timestamp'] = time.strftime('%Y-%m-%dT%H:%M:%SZ',
time.gmtime())
params['Signature'] = self._get_aws_auth_param(params, self.key,
self.action)
return params

This prevents tuple lists being used for EC2 drivers, for example.

A solution here would be to add a _extend_parameters to the base connection object, make it work whether the parameters were a dict or a list, and then update all the parameter mutating parts of the codebase to use it.