5a67c0524e [tests] Fix intermittent rpc_net.py failure. (John Newbery)
Pull request description:
rpc_net.py would intermittently fail on Travis, probably due to assuming that two consecutive RPC calls were atomic. Fix this by trying the test up to three times and only failing if all three attempts fail. fixes #11778
Tree-SHA512: f2f5047e05114ad2110377e6221ce057680c240952971fb33863834587d2250896c6b697ba27eef739cd0ab23faf47dfae8cafadc9833cbfab5a6f7e36dae5e2
Backport of Core PR12804
https://github.com/bitcoin/bitcoin/pull/12804/files