ASGARD-1117 - Prevent double form submission

It's common for people to click a submit button twice by accident or 
due to impatience. When that happens for a case like Create Next ASG,
a second task will be created and will fail because the ASG name is 
already taken. These errors are distracting, useless noise for the
user, the task list, the log, and Asgard developers.