Implement usermap exponential backoff (INF-1310)

[williamnswanson]

Update usermap script to use exponential backoff. The minimum and maximum timeouts can be set with options.

[brianhlin]

This would get the job done but I'm more interested in actually implementing an exponential timeout: try 5, 25, 125, and 625 seconds and then give up. I'm also fine if it's not configurable via option

[brianhlin]

Oh wait, I guess that is exponential! It's a little complicated but it'll do

Brian can't read code

[brianhlin]

I also updated the PR title (see https://osg-htc.org/technology/software/git-software-development/#summarize-your-commits-in-the-pull-request-title), partially because the title makes its way into the merge commit so we want it to summarize the changes in a human-readable way. Also, Jira will look for the ticket key in commits/title so you want that to be well-formatted

[brianhlin]

LGTM!