cloudforce.com instance issue

[Kevmo92]

When an instance is on the cloudforce.com domain of salesforce, the added .salesforce.com in the session class breaks interacting with the org.

This could be fixed by changing the SfdcSession.get_server_url() method to look like:

    def get_server_url(self):
        if not self._instance:
            url = SfdcSession._LOGIN_URL.format(**{'instance': 'test' if self._is_sandbox else 'login'})
        url = SfdcSession._LOGIN_URL.format(**{'instance': self._instance})
        if re.search(r'cloudforce', url):
            url = re.sub(r'\.salesforce\.com$', '', url)
        return url