Increase throughput performance of some serialized actions

[alfpark]

Leverage concurrent.futures for async submissions of lists of work.

• del certs
• add ssh user
• add rdp user
• del ssh user
• del rdp user
• reboot nodes
• delete tasks (both request and wait)
• term tasks (both request and wait)
• nodes grls (speed up generate ssh tunnel script with rls cache)
  • ensure consistent cardinality of results
  • add no generate ssh script option
• get all task files
• get all node files
• add task collection (along with bugfix from Task submission speed regression with many unnamed tasks or via task factory #183)
• recurrent job manager
• task file mover