Merge #13201: [qa] Handle disconnect_node race

Summary:
09c6699900 [qa] Handle disconnect_node race (Suhas Daftuar)

Pull request description:

Several tests call disconnect_nodes() on each node-pair in rapid
succession, resulting in a race condition if a node disconnects a peer
in-between the calculation of the nodeid's to disconnect and the
invocation of the disconnectnode rpc call.  Handle this.

Tree-SHA512: 3078cea0006fcb507c812004a777c505eb1e9dda7c6df12dbbe72395a73ff6f6760f597b6492054f5487b34534417ddef5fbad30553c135c288c4b7cfce79223

Backport of Core PR13201
https://github.com/bitcoin/bitcoin/pull/13201/

Test Plan:

test_runner.py

Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D4119