Test ulimit from a script

[pgarg66]

No description provided.

[mvines]

I adjusted the ci-large agent config (#570 (comment)):

open files                      (-n) 65536

Let's add something like this to ci/test-large-network.sh:

if [[ $(ulimit -n) -le 65000 ]]; then
  echo 'Error: nofiles too small, run "ulimit -n 65000" to continue'
  exit 1
fi

[pgarg66]

Sounds good. I'll push the script change as part of my other patch.
Closing this PR.