stress.py with network proxy

[SkidanovAlex]

We want to add various workers into stress.py that interfere with the network.

There's already an attempt to build such a worker (see local_network in the test), but that requires a certain machine setup, which can be avoided with the new proxying infrastructure.

What we want:

1. Remove the existing network infra from the stress.py;
2. Change local_network mode to use proxies (proxify each node, and make local_network block all messages to and from a particular node for some brief amount of time);
3. Add a new worker drop_messages that instead of completely isolating a node just drops a certain percentage of messages between each pair of nodes;

We want eventually the following tests to pass:

pytest --timeout=2000 stress/stress.py 3 3 3 0 staking transactions local_network
pytest --timeout=2000 stress/stress.py 3 3 3 0 staking transactions drop_messages

(the arguments to stress.py are number of shrads, number of nodes initially, number of nodes max, number of observers, workers).

[SkidanovAlex]

This now only tracks local_network.

#3105 and #3106 track other network-related modes.

[SkidanovAlex]

Michael already started it here: #3076

Locally it currently fails hitting RPC timeouts.

Reassigning to Marcelo so that Michael can concentrate on mocknet tests.

[SkidanovAlex]

The local_network mode is moderately stable in master now, closing this issue