Logs into the cimc device and returns the session cookie.

def logon():
    '''
    Logs into the cimc device and returns the session cookie.
    '''
    content = {}
    payload = "<aaaLogin inName='{0}' inPassword='{1}'></aaaLogin>".format(DETAILS['username'], DETAILS['password'])
    r = __utils__['http.query'](DETAILS['url'],
                                data=payload,
                                method='POST',
                                decode_type='plain',
                                decode=True,
                                verify_ssl=False,
                                raise_error=False,
                                status=True,
                                headers=DETAILS['headers'])

    _validate_response_code(r['status'])

    answer = re.findall(r'(<[\s\S.]*>)', r['text'])[0]
    items = ET.fromstring(answer)
    for item in items.attrib:
        content[item] = items.attrib[item]

    if 'outCookie' not in content:
        raise salt.exceptions.CommandExecutionError("Unable to log into proxy device.")

    return content['outCookie']