Add parse_url to _utils.

The patch adds parse_url to _utils as an attempt to find a common url
format that satisfies most drivers needs. The code isn't definitive but
instead the beginning for further discussions. Current code parses
transport urls like this:

qpid://test/test
{'exchange': 'test',
 'hosts': [{'host': 'test', 'password': '', 'username': ''}],
 'parameters': {},
 'transport': 'qpid'}

qpid://test:port/test
{'exchange': 'test',
 'hosts': [{'host': 'test:port', 'password': '', 'username': ''}],
 'parameters': {},
 'transport': 'qpid'}

qpid://username:password@test:port/test
{'exchange': 'test',
 'hosts': [{'host': 'test:port',
            'password': 'password',
            'username': 'username'}],
 'parameters': {},
 'transport': 'qpid'}

qpid://username:password@test:port
{'exchange': None,
 'hosts': [{'host': 'test:port',
            'password': 'password',
            'username': 'username'}],
 'parameters': {},
 'transport': 'qpid'}

qpid://username:password@test:port,test2:port2/test
{'exchange': 'test',
 'hosts': [{'host': 'test:port',
            'password': 'password',
            'username': 'username'},
           {'host': 'test2:port2',
            'password': 'password',
            'username': 'username'}],
 'parameters': {},
 'transport': 'qpid'}

qpid://username:password@test:port,:@test2:port2/test
{'exchange': 'test',
 'hosts': [{'host': 'test:port',
            'password': 'password',
            'username': 'username'},
           {'host': 'test2:port2', 'password': '', 'username': ''}],
 'parameters': {},
 'transport': 'qpid'}

qpid://username:password@test:port,:@test2:port2/test?option=value
{'exchange': 'test',
 'hosts': [{'host': 'test:port',
            'password': 'password',
            'username': 'username'},
           {'host': 'test2:port2', 'password': '', 'username': ''}],
 'parameters': {'option': ['value']},
 'transport': 'qpid'}

"qpid:///test"
{'hosts': [], 'parameters': {}, 'transport': 'qpid', 'exchange': 'test'}