new thread-based ssh system hammers nodes

[Zachary Ulissi]

The new thread-based starter for the parallel worker session is great, and startup is much faster now!

However, it's too fast, and our nodes can't keep up with all the SSH connections simultaneously (16/node). Adding a brief pause (0.5 seconds works, maybe even less is sufficient) after each thread.start() is sufficient for things to work normally.

Easy fix:

for thread in threads: thread.start() time.sleep(0.5)

[andrew_peterson]

Fixed in commit 8f01217