Signed-off-by: Guohan Lu <lguohan@gmail.com>

- Adding support for subscribe mode. The code is mostly based on this patch: #65
- Adding a new parameter to limit the number of updates, e.g. after a number of streaming updates the client would stop listening. It is convenient for testing purposes.
- Changing the sample interval unit to millisecond. This is also required for testing cases.

Co-authored-by: Murat Acikgoz <muacikgo@microsoft.com>

What is the motivation of this PR?
This PR aims to trigger memory spike on gNMI server side without explicitly closing the channels (TCP connections) from gNMI client side.

How did you do it?
I added an option --trigger_mem_spike in this python client script such that the user can specify this option to trigger memory spike.

How did you test/verify it?
I verify this on the ptf docker container binding to the lab device str-s6000-acs-11. The command line I used is as following:
python /gnxi/gnmi_cli_py/py_gnmicli.py -g -t *.*.*.* -p 50051 -m subscribe -x DOCKER_STATS,TEST_STATS -xt STATE_DB -o "ndastreamingservertest" --trigger_mem_spike

Signed-off-by: Yong Zhao <yozhao@microsoft.com>

What is the motivation of this PR?

This PR adds support for testing structured events as part of nightly test, by adding params: filter_event and event_op_file
When subscribing to EVENTS/all we will check for filter_event as part of response and then we will add response that contains filter to op_file. Test will then fetch this output file then do parsing logic for yang validation.

How did you do it?

I added options filter_event and event_op_file for supporting nightly tests for event

How did you test/verify it?

I verify this on the ptf docker container binding to the lab device str-s6000-on-6. The command line I used is as following:
python /gnxi/gnmi_cli_py/py_gnmicli.py -g -t ... -p 50051 -m subscribe -x all -xt EVENTS -o "ndastreamingservertest" --filter_event_regex sonic-events-bgp:bgp-state

1. Upgrade grpcio and grpcio-tools
2. Support origin in gnmi prefix
3. Print grpc error code
4. Support PROTO encoding for gnmi get
5. Ignore / in []
6. Support proto_bytes for gnmi set
7. Support multiple path and value for gnmi set, get and subscribe