support rest-proxy URI

[chen23]

iWorkflow / BIG-IQ (?) support REST proxy URI. This makes it possible to apply tenant RBAC on the REST endpoints (i.e. limit a user to only be able to modify a single BIG-IP LTM pool in a single Partition).

Documented here: https://devcentral.f5.com/wiki/iControl.REST_proxy_APIs.ashx

Example of one of the changes required (this is not meant to be a "good" example, but it gets the job done). This was done to monkey patch the library:

def _validate_icruri(base_uri):
    # The icr_uri should specify https, the server name/address, and the path
    # to the REST-or-tm management interface "/mgmt/tm/"
    scheme, netloc, path, _, _ = urlsplit(base_uri)
    if scheme != 'https':
        raise InvalidScheme(scheme)
    if path.startswith('/mgmt/shared/'):
        return icontrol.session._validate_prefix_collections(path[9:])
    if not path.startswith('/mgmt/tm/'):
        error_message = "The path must start with '/mgmt/tm/'!!  But it's:" +\
            " '%s'" % path[:10]
        raise InvalidBigIP_ICRURI(error_message)
    return icontrol.session._validate_prefix_collections(path[9:])
icontrol.session._validate_icruri = _validate_icruri